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THE    PUBLOW   ACID   TEST 


Questions  and  Answers 
on  Milk  and  Milk-Testing 


By 
CHAS.  A.  PUBLOW,  A.B.M.D.CM. 

Assistant  Professor  of  Dairy   Industry  in 
Cornell  Uni<versity 

And 
HUGH  G.  TROY,  B.  S.  A. 

Agricultural  Chemist  for  the  Neiv  York   State 
Department  of  Agriculture 


ILLUSTRATED 


NEW    YORK 

ORANGE  JUDD  COMPANY 

LONDON 

Kegan  Paul,  Trench,  Trubner  &  Co.,  Limited 
1913 


Copyright,  1909 

Orange  Judd  Company 

New  York 


tBXmSED  AT  STATIOITEBS'  HAIJ.,  LOWDOH,  ■WOI.AHD] 


Printed  in  U.  S.  A. 


In  compliance  with  current  copyright  law,  Etherington 

Conservation  Services  produced  this  replacement  volume 

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PREFACE 

Anyone  who  has  had  experience  in  teaching 
short-course  students  in  dairying  realizes  the  dif- 
ficulty most  of  these  students  have  in  taking  notes 
and  in  preparing  for  examinations.  Many  of  these 
men  and  boys  are  good  cheese  and  butter  makers, 
but  through  lack  of  preliminary  education  they 
are  unable  to  successfully  place  on  paper  the 
knowledge  they  really  possess. 

It  is  for  these  men  more  particularly  that  the 
authors  have  prepared  this  little  book. 

All  up-to-date  dairy  literature  has  been  freely 
consulted  with  the  hope  of  making  these  question 
compends  of  the  greatest  service.  Many  new  facts 
that  have  never  appeared  in  any  dairy  books  have 
been  added  and  written  in  simple  language.  The 
special  work  on  adulterations  should  be  of  consid- 
erable value  to  dairy  instructors  and  to  those  who 
wish  to  prepare  for  civil  service  examinations  for 
state  positions  in  dairy  work. 

It  is  the  intention  of  the  authors  to  keep  this 
book  strictly  up  to  date,  and  they  will  be  grateful 
to  all  readers  who  may  suggest  any  corrections  or 
improvements  that  might  be  made  to  further  the 
usefulness  of  the  book. 

CHAS.  A.  PUBLOW 
HUGH  C.  TROY 

September,  1909 


Questions  and  Answers  on  Milk 
and  Milk-Testing 


What  is  the  average  composition  of  cow's  milk? 

Water    87.0% 

Fat 4.0% 

Sugar 5.0% 

Casein   2.6% 

Albumin 7% 

Ash 7% 

100.0% 

How  does  the  composition  of  cow's  milk  compare 
with  the  composition  of  human  milk? 
Human  milk  contains  more  sugar,  less  casein  and 
albumin  and  less  ash.     Konig  gives  the  following 
composition  of  human  milk: 

Water    87.41% 

Fat   3.78% 

Sugar  6.21  % 

Casein  and  albumin      2.29% 
Ash 31% 

100.00% 

The  specific  gravity  of  human  milk  is  lower  than 
cow's  milk,  being  about  1.027. 


2  QUESTIONS  AND  ANSWERS 

How  does  the  natural  water  in  milk  differ  from 
other  water? 
Well  water,  spring  water,  and  water  from  other 
sources  varies  considerably  in  composition.  So 
does  the  composition  of  water  in  milk.  But,  ordi- 
narily speaking,  water  in  milk  is  not  different  from 
other  fresh  water. 

In  what  form  does  fat  exist  in  milk? 

In  small  round  globules  held  in  suspension  and 
forming  an  emulsion  with  the  other  constituents. 
These  globules  vary  in  size  from— ^jq— to  ^^f^  of  an 
inch  in  diameter. 

What  can  be  seen  when  milk  is  examined  under  a 
high-power  microscope? 
Small   fat-globules   floating  around   in   the   milk 
serum. 

In  what  form  does  sugar  exist  in  milk? 
In  solution. 

What  is  the  composition  of  milk  sugar? 

Carbon    42.10% 

Hydrogen   6.72% 

Oxygen    5i-i8% 

In  what  form  does  ash  exist  in  milk? 

Part  in  suspension  and  part  in  solution. 

What  forms  of  mineral  ash  are  found  in  milk? 

Calcium,   sodium,   potassium,   phosphorus,   mag- 
nesium. 


ON    MILK   AND   MILK-TESTING  3 

In  what  form  does  casein  exist  in  milk? 
In  minute  particles  held  in  suspension. 

In  what  form  does  albumin  exist  in  milk? 
Albumin  is  in  solution. 

How  does  the  action  of  casein  differ  from  that  of 
albumin? 

Casein  is  in  suspension.  It  is  precipitated  by 
rennet  and  acids.     It  is  not  precipitated  by  heat. 

Albumin  is  in  solution.  It  is  not  precipitated  by 
rennet  and  acids,  but  is  precipitated  by  a  heat  of 
180°  F. 

What  is  the  composition  of  casein? 

Carbon    53-00% 

Oxygen   22.70% 

Nitrogen  1570% 

Hydrogen 7.00% 

Phosphorus    ...         .85% 
Sulphur 75% 

100.00% 

What  are  the  melting  points  of  the  important  fats  ? 

Olein    41°  F. 

Palmatin   142°  F. 

Myristin    129°  F. 

These  fats  become  oily  when  heated  and  solidify 
on  cooling,  some  fats  sooner  than  others. 

What  is  the  specific  gravity  of  fat? 
About  .93. 


QUESTIONS   AND  ANSWERS 


Of  what  is  milk  fat  formed? 
Fatty  acids  and  glycerin. 


Volatile  - 


Non- 
volatile 


What  fats  are  present  in  milk? 

'Butyrin   3-85% 

Caproin   3.60% 

^Caprylin 55% 

'Olein    35-oo% 

Palmatin 25.70% 

Myristin    20.20% 

Laurin 740% 

Caprin   1.90% 

^Stearin 1.80% 

100.00% 

What  is  a  volatile  fat? 

One  composed  of  a  soluble  volatile  fatty  acid  and 
glycerin. 

What  is  a  non- volatile  fat? 

One  composed  of  an  insoluble  non-volatile  fatty 
acid  and  glycerin. 

What  factors  influence  the  size  of  fat-globules  in 
milk? 

1.  Breed  of  the  cow. 

2.  Individuality  of  the  cow. 

3.  Character  of  the  food. 

4.  Period  of  lactation. 

5.  Age  of  the  cow. 

6.  Diseased  conditions. 

7.  The  part  of  the  milk  examined. 


ON  MILK  AND  MILK-TESTING  5 

What  is  the  theory  of  an  envelope  surrounding  fat- 
globules? 

Some  chemists  have  been  unable  to  find  any  such 
covering,  but  Storch  says  he  has  found  it  to  exist, 
and  that  it  is  composed  of  94  per  cent  water  and  64 
per  cent  proteids. 

How  is  the  acid  in  milk,  cream  starters,  or  butter- 
milk measured? 
By  an  acidimeter. 

Describe  an  acidimeter  and  the  method  of  testing. 

There  are  several  tests  for  measuring  acid,  and 
sold  on  the  market  under  different  names,  such  as 
Publow's,  Mann's,  Farrington's,  and  Marshall's,  but 
the  principle  is  the  same  in  all  of  them.  An  alka- 
line solution  of  known  strength  and  an  indicator 
called  phenol-phthalein  are  the  reagents  used.  The 
purpose  of  the  indicator  is  to  indicate  the  reaction 
of  the  milk  or  cream ;  that  is,  it  shows  whether  the 
milk  or  cream  is  acid,  alkaline,  or  neutral.  The 
indicator  has  no  color  effect  in  an  acid  solution, 
but  it  turns  an  alkaline  substance  red.  .  When  the 
neutral  point  is  reached,  the  faintly  pink  color  is 
barely  distinguishable. 

To  make  the  test:  A  known  qtfantity  of  the 
milk  or  cream  to  be  tested  is  placed  in  a  white  cup. 
To  this  a  few  drops  of  indicator  are  added.  An 
alkaline  solution  of  known  strength  is  then  allowed 
to  run  in,  drop  by  drop,  from  a  graduated  burette 
until  the  milk  or  cream  assumes  a  faintly  pink 
color,  which  signifies  that  all  the  acid  in  the  milk 
or  cream  has  been  neutralized  by  the  alkali  used. 
The  amount  of  alkali  used  can  be  read  on  the 


6  QUESTIONS   AND  ANSWERS 

burette,  and,  as  its  strength  is  known,  it  is  an  easy 
matter  to  figure  the  amount  of  acid  in  the  milk  or 
cream. 

One  c.  c.  of  Yiq  normal  alkali  neutralizes  .009 
gram  lactic  acid. 

In  the  test  used  at  Cornell  university  the  alkali 
used  is  a  %o  normal  solution  of  caustic  soda.  This 
makes  a  very  convenient  strength,  because  when  9 
grams  of  cream  or  milk  are  taken  .1  c.  c.  of  it  neu- 
tralizes or  represents  .01  per  cent  lactic  acid.  Thus, 
if  in  testing  the  milk  4  c.  c.  of  the  alkali  isoised,  the 
milk  contains  .40  per  cent  of  acid. 

In  Farrington's  test  the  alkali  used  is  made  %o 
normal  by  adding  5  tablets  in  97  c.  c.  water.  Then 
when  17.6  c.  c.  milk  is  taken,  i  c.  c.  of  the  alkali 
represents  .01  per  cent  acid. 

In  Mann's  test  a  Yio  normal  alkali  is  used  and 
50  c.  c.  of  milk  is  tested.  The  number  c.  c.  of 
alkali  necessary  to  neutralize  the  acid  measures  in 
degrees  the  amount  of  acid. 

One  c.  c.  of  -5-  alkali=i  degree  Mann's  test. 

To  get  the  per  cent  acid  multiply  the  number  c.  c. 
alkali  used  by  .009,  divide  by  50  and  multiply  by 
100. 

How  can  milk  or  cream  be  tested  on  the  receiving 
platform? 

1.  For  acidity  by  the  use  of  an  acidimeter. 

2.  For  odors  by  sense  of  smell. 

3.  For  flavors  by  sense  of  taste. 

4.  For  insoluble  dirt,  by  eyesight  and  by  allow- 
ing samples  to  stand  a  few  minutes  in  small  glass 
jars  so  that  the  dirt  will  settle  to  the  bottom. 


ON    MILK   AND   MILK-TESTING  7 

5.     In  cold  weather  flavors  and  odors  can  be  de- 
tected more  readily  if  milk  and  cream  is  warmed  up 
by  steam. 
.  6.     By  the  use  of  a  fermentation  test. 

7.  For  adulteration  by  the  use  of  a  lactometer. 

8.  Samples  can  be  taken  for  fat-testing  in  the 
Babcock  test. 

Where  is  milk  secreted? 

In  the  mammary  glands  of  all  mammals  which 
suckle  their  young. 

Describe  a  mammary  gland  system  of  a  cow. 

A  cow  possesses  two  mammary  glands  situated 
on  either  side  of  the  median  line  of  the  body  on  the 
under  and  hind  part,  and  each  gland  is  divided  into 
two  parts,  called  lobes.  Each  gland  is  composed  of 
glandular  tissue,  being  constructed  largely  of  blood 
vessels  and  epithelial  cells.  Each  of  the  four  lobes 
has  a  small  duct  opening  through  which  milk  is 
carried  after  secretion  to  the  teat  outlets. 

Describe  the  udder  of  a  cow. 

The  udder  is  the  milk  reservoir  of  the  cow,  and 
is  situated  between  her  hind  legs  on  the  posterior 
part  of  the  abdomen.  It  varies  in  size  and  shape 
and  also  in  structure.  The  udder  is  composed  of 
glandular  tissue  such  as  fatty  tissue,  milk  ducts  and 
canals,  secreting  cells,  arteries,  veins,  lymphatics, 
nerves,  and  connective  tissue  which  binds  all 
the  other  tissues  together.  The  glands  are  sup- 
ported from  the  abdomen  by  a  heavy  band  of 
fibrous  tissue  which  extends  from  the  abdomen 
through  the  udder  in  the  median  line.    The  whole 


8  QUESTIONS   AND  ANSWERS 

mass,  which  is  more  or  less  grayish  red  in  color, 
according  to  its  varied  structure,  is  covered  on  the 
outside  by  a  heavy  fold  of  skin  which  is  covered 
with  fine  hair  and  has  marked  elasticity. 

Internally  the  udder  is  divided  into  four  quar- 
ters, the  two  quarters  on  the  same  side  communi- 
cating with  each  other  and  each  quarter  being  sup- 
plied with  an  outlet  or  teat. 

At  the  upper  end  of  each  teat  is  a  fairly  large 
cavity  called  a  milk  cistern,  each  of  which  may  hold 
as  much  as  one-half  pint.  In  these  the  milk  col- 
lects after  being  secreted  and  carried  from  the 
glandular  cells  by  a  more  or  less  complicated  series 
of  milk  ducts  and  canals.  At  the  lower  end  of 
each  teat  a  circular  muscle  exists,  which,  when  con- 
tracted, has  the  power  of  closing  the  lower  opening 
and  preventing  the  escape  of  milk. 

Considerable  muscular  tissue  exists  in  the  udder, 
especially  around  the  walls  of  milk  ducts  and  their 
dividing  points.  These  muscles  are  well  supplied 
with  nerves  so  that  the  animal  can  by  her  will 
power  control  to  a  considerable  extent,  for  a  short 
time,  the  evacuation  of  milk  after  it  has  been 
secreted  by  the  small  cells.  She  cannot,  however, 
control  the  actual  secreting  process.  The  milk- 
producing  power  of  an  udder  depends  largely  upon 
the  amount  of  blood  carried  to  and  from  it  through 
the  arteries  and  veins. 

How  and  from  what  is  milk  secreted? 

Milk  is  secreted  from  the  blood  while  it  passes 
through  the  smallest  blood  vessels  in  the  udder 
called  the  capillaries  and  from  the  lymph  while  it 
passes  through  the  lymphatics. 


ON    MILK   AND    MILK-TESTING  9 

The  water,  albumin,  casein,  and  ash  all  come 
directly  from  the  blood  stream  being  more  or  less 
changed  as  they  pass  through  the  very  thin  walls 
of  the  capillaries  and  by  the  action  of  the  glandular 
cells.  The  sugar  is  formed  from  the  blood.  The 
fat  is  derived  from  the  breaking  down  of  the  gland 
cells  by  a  process  of  fatty  degeneration  and  from 
the  lymph  stream.  The  amount  of  milk  secreted 
depends  upon  the  amount  and  composition  of  the 
blood  and  lymph  carried  to  and  from  the  udder 
in  a  given  time  and  also  upon  the  activity  of  cell 
construction  and  cell  destruction  in  the  mammary 
glands. 

What  is  colostrum? 

Colostrum,  or  beastings,  is  the  first  milk  secreted 
by  a  cow  after  the  birth  of  her  calf. 

What  is  the  average  composition  of  colostrum? 
(Konig.) 

Water    74-6% 

Fat 3.6% 

Casein    4.0% 

Albumin   13-6% 

Sugar 2.7% 

Ash   1.5% 

The  composition  of  colostrum  varies  in  individ- 
ual cows  to  such  an  extent  that  only  an  average 
composition  can  be  given. 

How  does  colostrum  differ  in  composition   from 
ordinary  milk? 
Colostrum  contains  less  water,  less  fat,  less  sugar, 
more  casein,  more  albumin,  and  more  ash.  It  is  higher 


lO  QUESTIONS  AND  ANSWERS 

in  color  and  strong  in  odor,  and  has  a  laxative 
effect  upon  the  bowels  of  the  calf.  Varied  amounts 
of  blood  and  broken-down  cells  are  usually  present, 
and  the  viscosity  is  greater.  The  specific  gravity 
is  also  higher  and  colostrum  is  unfit  for  human 
consumption.  Examined  under  the  microscope, 
large  colostrum  corpuscles  can  be  seen. 

By  what  tests  can  colostrum  be  detected? 

1.  By  the  use  of  a  lactometer,  which  shows  a 
very  high  specific  gravity. 

2.  Boiling  throws  down  a  large  amount  of  al- 
bumin. 

3.  Examined   under  the   microscope,   colostrum 
corpuscles  can  be  seen. 

What  is  the  natural  color  of  milk  due  to? 

1.  To  lactochrome. 

2.  To  the  color  of  the  milk  fats,  especially  pal- 
matin. 

What  is  milk  serum? 

The  serum  of  milk  is  that  part  which  is  left  after 
all  fat  has  been  removed. 

What  factors  influence  the  composition  of  milk? 

1.  Breed  of  the  cow. 

2.  Individuality  of  the  cow. 

3.  Period  of  lactation. 

4.  Time  of  milking. 

5.  Part  of  milk  tested. 

6.  Health  of  the  cow. 

7.  Food  and  water  consumed  by  the  cow. 


ON    MILK   AND   MILK-TESTING  II 

What  ferments  are  present  in  milk? 

1.  Organized  (Bacteria). 

2.  Unorganized  (Galactase). 

What  is  the  difference  between  an  organized  and 
an  unorganized  ferment? 

An  organized  ferment  is  due  to  the  action  of  bac- 
teria and  has  the  power  of  reproducing  itself. 

An  unorganized  ferment  or  enzyme  is  formed  by 
the  action  of  glandular  tissue  and  has  not  the  power 
of  reproducing  itself,  although  its  action  may  not 
be  destroyed  after  performing  its  function.  As  an 
example  of  this  we  have  rennet,  which  does  not  los»e 
its  power  after  coagulating  milk. 

What  are  bacteria? 

They  are  the  lowest  forms  of  microscopical  plant 
life,  and  are  composed  of  protoplasm. 

What  are  spores? 

A  spore  is  the  breeding  cell  of  a  bacterium.  All 
bacteria  do  not  form  spores,  many  reproducing  by 
a  process  known  as  "  fission,"  the  cell  simply  divid- 
ing into  two  or  more  parts  or  bacteria. 

What  are  the  three  necessities  for  bacterial  growth? 

1.  Suitable  food. 

2.  Moisture. 

3.  A  proper  temperature. 

What  bacteria  are  commonly  found  in  milk? 

I.  Those  that  sour  milk,  called  lactic  acid  bac- 
teria. 


12  QUESTIONS  AND  ANSWERS 

2.  Those  that  produce  gas  and  bad  flavors  in 
milk,  called  putrefactive  bacteria. 

3.  Those  that  produce  disease  called  pathogenic 
bacteria. 

4.  Specific  bacteria,  such  as  those  producing 
blue  milk,  bitter  milk,  ropy  milk,  etc. 

How  do  bacteria  gain  entrance  to  milk? 

1.  From  the  air.  The  purity  of  the  air  deter- 
mines the  number  and  character  of  the  bacteria. 
The  air  in  unclean  stables  contains  many  bacteria. 

2.  From  dirt  or  dust.  All  dirt  and  all  dust  carry 
many  bacteria,  mostly  of  the  putrefactive  type. 

3.  From  the  hands,  clothing,  or  body  of  persons 
that  have  or  recently  have  had  or  are  caring  for 
persons  who  have  contagious  or  infectious  diseases. 

4.  From  unclean  utensils. 

5.  From  infected  water  supply. 

6.  From  diseased  cows. 

What  effects  do  bacteria  produce  in  milk? 

1.  Some  forms  sour  milk. 

2.  Some  forms  produce  gas  in  milk. 

3.  Some  produce  undesirable  flavors. 

4.  Some  cause  sweet  coagulation. 

5.  Some  cause  ropy  milk. 

6.  Some  cause  bitter  milk. 

7.  Some  produce  abnormal  colors  in  milk. 

8.  Some  carry  disease  and  render  milk  unfit  for 
consumption. 

How  is  the  bacterial  content  of  milk  controlled? 

I.  By  absolute  cleanliness  in  all  things  sur- 
rounding the  production  and  handling  of  the  milk. 


ON    MILK  AND   MILK-TESTING  I3 

This  tends  to  prevent  the  entrance  of  bacteria  into 
milk. 

2.  By  keeping  milk  cold.  This  checks  the 
growth  of  bacteria.  The  lower  the  temperature,  the 
more  their  growth  is  prevented  and  the  longer  will 
milk  keep  sweet. 

3.  By  high  temperatures.  High  temperatures 
are  used  to  destroy  bacterial  life  in  milk.  This  is 
the  principle  of  pasteurization. 

4.  Preservatives  are  used  to  kill  bacteria  or  to 
prevent  their  growth.  The  use  of  preservatives  in 
milk  is  prevented  by  most  pure  food  laws. 

5.  Electricity  has  been  used  to  destroy  bacteria 
in  milk. 

6.  The  use  of  carbonic  acid  gas  is  used  to  car- 
bonate milk  and  prevent  the  growth  of  bacteria. 

What  methods  are  used  to  keep  bacteria  out  of 
milk? 
I.     The  health  of  the  cows  is  considered.     The 
tuberculin   test    is   used   to   diagnose   tuberculosis. 
Milk  from  diseased  animals  is  not  used. 

•  2.     Cows*  udders,  flanks,  and  legs  are  shorn  of 
hair  to  make  cleaning  easy. 

3.  These  parts  are  washed  or  wiped  with  a 
damp  cloth  before  milking. 

4.  Stables  are  properly  ventilated,  made  free 
from  dust,  whitewashed,  or  otherwise  made  sani- 
tary by  cleanly  methods. 

5.  The  health,  clothing,  hands,  and  person  of  the 
milkers  are  regulated  in  sanitary  requirements. 

6.  Small-top  milking  pails  are  used. 

7.  Milk  is  strained  or  filtered  in  a  clean  place. 


14  QUESTIONS   AND   ANSWERS 

8.  Cans,  bottles,  and  all  utensils  are  sterilized 
before  use. 

9.  Milk  is  bottled  to  prevent  the  entrance  of  air 
and  bacteria. 

10.  Milk  is  cooled  to  low  temperature  as  soon 
as  drawn,  and  kept  cold  to  prevent  bacterial 
growth. 

How  can  bacteria  in  milk  be  destroyed? 

1.  By  heating  to  a  high  temperature  for  a  time. 
Some  forms  are  killed  in  ten  minutes  at  140°  F., 
while  others  require  a  much  higher  temperature  for 
a  longer  period. 

2.  By  electricity. 

3.  By  the  use  of  certain  poisons  which  destroy 
bacterial  life. 

What  diseases  are  carried  in  milk? 

1.  Typhoid  fever. 

2.  Scarlet  fever. 

3.  Diphtheria. 

4.  Tuberculosis. 

5.  Intestinal  infections,  such  as  the  cholera  of 
infants  and  dysentery  in  adults. 

How  do  the  germs  of  disease  enter  milk? 

1.  In  dust  laden  with  disease-producing  bac- 
teria. 

2.  From  the  body  or  clothing  of  milkers  who 
have  had  or  have  been  exposed  to  diseases  that 
are  contagious  or  infectious. 

3.  From  infected  water  used  in  washing  or  rins- 
ing cans  or  utensils. 


ON    MILK  AND   MILK-TESTING  1$ 

4.  From  diseased  cows, .  especially  when  the 
udder  is  diseased. 

5.  From  the  excreta  of  animals,  which  may 
enter  milk  in  small  particles  carrying  disease-pro- 
ducing bacteria. 

What  causes  milk  to  sour? 

The  lactic  acid  bacteria  change  the  milk  sugar 
into  lactic  acid,  which  is  sour  and  as  soon  as  suf- 
ficient acid  is  formed  the  whole  volume  of  milk 
becomes  sour  to  the  taste. 

What  are  the  causes  of  bad  flavors  in  milk? 

1.  Bacteria,  which  may  enter  milk  in  any  of  the 
following  ways: 

(o)  From  dust. 

(b)  On  dirt  from  the  body  of  the  cow. 

(c)  From  the  atmosphere. 

(d)  From  hands,  body,  or  clothing  of  persons 

handling  milk. 

(e)  From  dirty  utensils. 
(/)  From  impure  water. 
(g)  From  diseased  cows. 

2.  Flavors  absorbed  when  milk  is  exposed  in 
places  where  strong-smelling  substances,  such  as 
turnips  and  decayed  vegetables,  are  kept. 

3.  From  strong-smelling  foods  eaten  by  the  cow. 

4.  Keeping  milk  at  too  warm  a  temperature. 
When  milk  is  warm,  bacteria  present  grow  rapidly, 
and  their  action  on  the  different  constituents  of 
milk  produces  bad  flavors. 

How  should  milk  cans  and  utensils  be  washed? 
They    should    be    first    rinsed    with    lukewarm 


l6  QUESTIONS   AND   ANSWERS 

water,  then  washed  with  a  brush  and  hot  water 
containing  some  good  washing  powder.  Then 
boiling  water  or  steam  should  be  used  to  sterilize. 
The  utensils  should  then  be  placed  in  a  clean  place 
free  from  dust.  It  is  a  good  plan  to  expose  milk 
cans,  etc.,  to  the  direct  rays  of  the  sun,  which  have 
the  power  of  destroying  bacteria. 

What  is  pasteurization? 

It  is  the  heating  of  milk  to  at  least  140°  F.  for 
at  least  ten  minutes  for  the  purpose  of  destroying 
bacteria.  The  milk  is  then  usually  cooled  to  a  low 
temperature.  The  word  is  derived  from  Louis 
Pasteur,  an  eminent  French  scientist. 

What  is  sterilization? 

It  is  the  heating  of  milk  to  at  least  212°  F.  for 
the  purpose  of  destroying  both  bacteria  and  spores. 

How  is  milk  usually  pasteurized  for  commercial 
purposes? 

1.  By  some  form  of  pasteurizing  machine  in 
which  steam  is  the  heating  agent. 

2.  By  electricity. 

What  are  some  of  the  reliable  pasteurizing  machines 
on  the  market? 

1.  Simplex. 

2.  Miller-Tyson. 

3.  Farrington. 

4.  Wizard. 

5.  Reid. 


ON    MILK  AND   MILK-TESTING  I7 

How  can  buttermilk  be  prepared  from  skimmed 
milk? 
Skimmed  milk  is  heated  to  165°  F.  for  ten 
minutes  and  then  cooled  to  70°  F.,  when  about  5  per 
cent  of  a  good  culture  of  lactic  acid  is  added.  The 
milk  should  be  softly  coagulated  in  12  hours.  It  is 
then  churned  for  five  minutes  and  the  result  is  a 
fine  quality  of  buttermilk. 

How  are  the  fancy  acid  milk  drinks  prepared? 

By  pasteurizing  skimmed  milk,  then  cooling  and 
adding  cultures  of  some  acid-producing  bacteria 
or  yeasts.  The  milk  is  securely  bottled  to  prevent 
outside  contamination. 

What  is  market  milk? 

Milk  that  is  produced  and  marketed  solely  for  its 
use  as  milk. 

How  is  milk  marketed? 

Milk  in  its  raw  state  is  marketed  in  one  of  two 
ways,  (i)  In  bulk  form.  (2)  In  bottles  or  sealed 
vessels. 

Milk  is  sold  under  many  descriptive  and  yet  de- 
ceiving names,  such  as  aerated,  clarified,  modified, 
pasteurized,  standardized,  etc.  These  words  usually 
indicate  some  special  treatment  given  to  milk  by 
the  producer  or  dealer. 

What  is  sanitary  milk? 

Milk  that  is  produced  under  sanitary  conditions. 

What  is  aerated  milk? 

Milk  that  has  been  exposed  to  the  air  for  the  pur- 
pose of  cooling  it  or  allowing  animal  odors  to  pass 


1 8  QUESTIONS  AND  ANSWERS 

off.  Many  forms  of  aerating  devices  are  used  for 
this  purpose,  but  aeration  has  many  disadvantages 
and  practically  no  advantages  in  the  production  of 
clean,  sweet  milk. 

What  is  clarified  milk? 

Milk  that  has  been  run  through  a  separator  or 
centrifugal  machine  for  the  purpose  of  removing 
insoluble  dirt.  This  process  has  few  beneficial  ef- 
fects on  milk.  It  is  much  better  to  keep  dirt  out 
of  milk  in  the  first  place  than  try  to  remedy  the  evil 
later. 

What  is  modified  milk? 

Milk  that  is  modified  for  some  special  purpose, 
such  as  infant  feeding,  by  the  addition  of  such 
agents  as  lime  water  and  barley  water,  or  by  the 
removal  of  part  of  the  fat  or  casein. 

What  is  electrified  milk? 

Milk  that  has  been  treated  by  a  current  of  elec- 
tricity for  the  purpose  of  destroying  bacteria. 

What  is  pasteurized  milk? 

Milk  that  has  been  heated  to  a  high  temperature 
(at  least  140°  F.)  for  a  period  of  time  for  the  pur- 
pose of  destroying  bacteria.  The  milk  is  usually 
cooled  immediately  to  at  least  50°  F.  in  order  to 
increase  its  keeping  power.  A  great  deal  of  the 
milk  consumed  in  the  larger  cities  is  treated  in  this 
manner,  as  it  is  a  necessary  way  for  the  present 
at  least,  of  remedying,  in  part,  defects  in  milk 
caused  by  carelessness. 


ON    MILK   AND    MILK-TESTING  I9 

What  is  carbonated  milk? 

Milk  that  has  been  treated  with  carbonic  acid 
gas  for  the  purpose  of  preserving  it. 

What  is  malted  milk? 

Milk  that  has  been  heated  to  a  high  temperature 
for  the  purpose  of  killing  bacteria,  partly  con- 
densed and  then  a  small  quantity  of  malt  added. 

What  is  peptonized  milk? 

Milk  to  which  some  pepsin  has  been  added  for 
the  purpose  of  making  milk  more  easily  digestible. 
The  pepsin  may  be  added  to  whole  milk,  or  the  milk 
may  first  be  partly  condensed. 

What  is  condensed  milk? 

Milk  from  which  a  large  amount  of  water  has 
been  extracted  by  some  process  of  evaporation. 
Sometimes  cane  sugar  is  added  for  making  what  is 
known  as  sweetened  condensed  milk. 

What  is  the  composition  of  unsweetened  condensed 
milk?     (Konig.) 

Water    58.99% 

Fat  12.42% 

Casein  and  albumin.  11.92% 

Milk  sugar i449% 

Ash    2.18% 

What  is  the  composition  of  sweetened  condensed 
milk?     (Konig.) 

Water    25.61% 

Fat  10.35% 

Casein  and  albumin.      11.79% 


20  QUESTIONS  AND   ANSWERS 

Milk  sugar 13.84% 

Cane   sugar    36.22% 

Ash    2.19% 

What  is  milk  powder? 

Milk  that  has  been  evaporated  to  dryness  and 
then  placed  in  a  machine  which  reduces  the  dried 
milk  to  a  finely  powdered  condition. 

What  is  standardized  milk? 

Most  states  have  a  standard  of  quality  to  which 
milk  must  comply  before  being  sold  as  whole  milk. 
Some  states  have  a  law  which  requires  that  milk 
must  contain  at  least  3.5  per  cent  fat  and  at  least 
12  per  cent  total  solids.  Some  breeds  of  cows  do 
not  give  milk  that  tests  that  high,  so  it  is  necessary 
to  add  some  cream  or  take  away  some  skim  milk. 
This  process  is  known  as  standardizing.  At  the 
same  time,  in  some  states,  milk  must  comply  with 
a  law  which  says  milk  must  not  be  adulterated. 

How  can  the  amount  of  milk  or  cream  necessary 
for  standardizing  be  determined? 
This  problem  has  been  made  easy  by  the  use  of  a 
formula  and  square  devised  by  R.  A.  Pearson,  com- 
missioner of  agriculture  in  New  York  state.  Draw 
a  square  and  write  at  the  two  left-hand  corners  the 
percentages  of  fat  in  the  milk  and  the  cream  or 
skim  milk  that  is  to  be  mixed  with  it.  In  the  cen- 
ter write  the  percentage  of  fat  desired.  The  dif- 
ference between  the  figures  in  the  center  and  the 
figures  at  the  left  are  placed  on  the  right-hand  cor- 
ners with  which  they  stand  in  line.  The  figures 
at  the  two  right-hand  corners  then  represent  the 


ON    MILK   AND   MILK-TESTING 


21 


proportions  in  which  the  milk  and  the  cream  or 
skimmed  milk  should  be  mixed. 

The  idea  can,  perhaps,  be  more  easily  understood 
by  working  out  a  problem  such  as  the  following: 

How  much  5  per  cent  milk  must  be  added  to  3.5 
per.  cent  milk  to  make  1,000  pounds  of  4  per  cent 
milk? 


.5     jI  X  1000  lbs.=333  lbs. 


5 

\  / 

.5 

4 

/  \ 

1.0 
l.S 


1.0 


1^  X  1000  lbs.=  666  lbs. 


The  milk  must  be  mixed  .5  part  of  5  per  cent 
milk  and  i.  part  of  3.5  per  cent  milk  in  every  1.5 
parts.  Therefore,  as  figured  above  we  must  mix 
333  pounds  of  5  per  cent  milk  and  667  pounds  of 
3.5  per  cent  milk  in  order  to  make  1,000  pounds  of 
4  per  cent  milk. 

Prof.  Oscar  Erf  has  also  prepared  a  table  to  be 
used  in  standardizing  milk  and  cream,  but  it  is  not 
necessary  to  give  it  here. 

V/hat  means  are  commonly  used  to  improve  the 
milk  supply  of  towns  and  cities? 

This  work  usually  is  conducted  under  direction 
of  the  boards  of  health.  In  most  places  all  per- 
sons delivering  milk  in  towns  and  cities  must  com- 
ply with  the  requirements  of  a  special  law  which 
states  that  all  milk  sold  must  be  produced  and 
handled  in  such  a  manner  that  it  reaches  the  con- 
sumer in  a  clean,  sanitary  condition. 

Inspectors  are  appointed  to  inspect  the  dairies 
and,  if  necessary,  compel  the  farmer  to  improve  his 


22  QUESTIONS  AND   ANSWERS 

dairy  methods.  Educational  means  are  used  as 
far  as  practicable,  but  if  any  man  refuses  to  com- 
ply with  the  sanitary  requirements  the  inspector 
reports  him  to  the  board  of  health,  which  usually 
cancels  his  license  and  prevents  him  selling  milk 
until  he  fulfils  the  demands  of  the  board. 

For  the  convenience  of  both  the  farmer  and  the 
inspector,  and  to  insure  uniform  inspections,  a 
score  card  is  used  upon  which  most  conditions  can 
be  reported. 

The  score  card  on  pages  24  and  25  is  the  one 
lately  devised  by  the  official  dairy  instructors'  as- 
sociation, and  which  is  now  most  used  in  the  United 
States. 

What  is  meant  by  specific  gravity? 

It  means  the  ratio  existing  between  the  weights 
of  equal  volumes  of  a  substance  and  water  at  4 
degrees  centigrade. 

Why  is  the  temperature  of  4  degrees  centigrade 
chosen? 
Because   water   reaches   its   greatest   density   at 
that  temperature. 

What  is  the  specific  gravity  of  whole  milk? 

The  average  is  about  1.032,  but,  in  some  cases,  it 
may  be  as  low  as  1.029,  or  it  may  go  as  high  as 
1.034 ;  that  is,  if  a  volume  of  water  weighs  1,000,  the 
same  volume  of  average  whole  milk  would  weigh 
1,032. 

How  would  you  calculate  the  weight  of  40  quarts 
milk? 


ON   MILK  AND   MILK-TESTING  23 

I  quart  water  weighs  946.4  grams. 
I  quart  milk  weighs  946.4X1.032  grams. 
453-6  gTams=i  pound. 
976.6848  grams=2.i53  pounds. 
I  quart  milk  weighs  2.153  pounds. 
40    quarts    milk    weigh    2.53X40    pounds=86.i2 
pounds. 

How  does  the  weight  of  40  quarts  milk  compare 
with  the  weight  of  40  quarts  water? 

I  quart  milk  weighs  2.153  pounds. 

I  quart  water  weighs  2.086  pounds. 

40  quarts  milk  weigh  86.12  pounds. 

40  quarts  water  weigh  83.44  pounds. 

The  weight  of  milk  is  1.032  times  as  great  as  the 
same  volume  water. 

What  substances  make  up  the  milk  serum? 

Water    87.0% 

Casein  and  albumin. .       3.4% 

Milk  sugar 5-0% 

Mineral  matter 7% 

What  is  the  specific  gravity  of  melted  milk  fat? 

Between  the  temperatures  of  120°  F.  and  160°  F. 
the  specific  gravity  is  .9;  that  is,  when  a  definite 
volume  of  water  weighs  1,000  the  same  volume  of 
milk  fat  weighs  900. 

What  common   proof  have  we   that   the   specific 
gravity  of  milk  fat  and  milk  serum  differs? 
When  milk  remains  quiet  for  a  time,  the  globules 
of  fat  rise  to  the  surface  in  the  form  of  cream. 


UNITED  STATES   DEPARTMENT  Or  AGRICULTURE. 

BUREAU  OF  ANIMAL  INDUSTRY, 

OAIRV   DIVISION. 


SANITIBY  INSPECTION  OF  DAIRIES. 


DAIRY   SCORE  CARD. 

Adopted  by  the  Official  Dairy  Instructors'  Assoclatloa 
(Subject  to  revision  at  future  meetioKs.) 


Owner  or  lessee  offarm ^ 

P.  0.  address  „ _    State. 

Total  number  of  cows Number  milking ^ 

Gallons  of  milk  produced  daily — _. _ 

Product  is  retailed  by  producer  in , 

Sold  at  wholesale  to 

For  milk  supply  of — „ _ 

Permit  No.  - -    Date  of  inspection  _ „ ,  J90 


Inspector. 
.m8-»-i-os-5.oa» 


DeTAiL.eD  scone. 


O0W8. 

Hetltb 

ApparentiT  In  Kood  hoaltb...  I 

If  iCKted  with  tubercuUn  onee 
o  year  and  no  tutxirculoFla 
h  found,  or  if  tested  once  In 
MX  months  and  all  reacttoK 
animals  removed S 

(II  tested  onlT  once  a  year  and 
rcartliiK  anlroali  found  and  re- 
mo  vul.  2.) 
Comfort 

BeddlDK 1 

Temperature  Of  atable. ..%...  I 

Food V 

Water 

Clean. I 

Fresh 1 

Light:  ioursq.  ft.  otxlasspercow 

(Thret  sq.  ft.,  3;  Stq.'ft..  3;  1 
CO.  ft.,  I.    Deduct  for  votfren  dia- 
trlbutloii ) 
VentilatlOD.  Automatic syatem... 

( Adjustable  windows,  1.) 
Cubic  feet  of  space  for  cow:  500 

to  1.000  leet 

(Less  than  fiOO  feet.  2 :  less  than 
400  feet.  1:  ics*  than  300  feet,  0.) 

STABLXS. 

Location  of  vUble 

Well  drained 1 


Constructifu  of  stable , 

Tisht,  sound  floor  and  proper 

gutter.^ 2 

Smootb,  tiebt  walla  and  ceU- 

mc 1 

Proper  stall,  tie.  and  manger.  1 

CTINSILS 

Construction  of  utensils , 

Water  (or  cleaning 

(Clean,  convenient,  and  abun- 
daiit.) 

Small-top  milking  paO 

Facilities  (or  hot  water  or  steam 

Milk  cooler 

Clean  nOking  suite «.. 


BAICPUNO  THS  MTUC 

Location  of  milk  room 

Free  from  contaminating  sur- 
roundings  1 

Convenient 1 

Construction  of  milk  room 

Floor,  walls,  and  ceiling 1 

Light  Teiitilation,  screens...  1 


ToUI. 


Perfect.    Allowelt. 


COWg  AXS  8TABLI8. 

Cleanliness  of  cows 

Cleanliness  of  stables 

Floor 2 

Walls 1 

Ceiling  and  ledges 1 

Mangers  and  partitions 1 

Windows 1 

Stable  air 

Barnyard  clean  and  welldrained. 
Removal  of  manure  dally   to 

field  or  proper  pit 

(To  60  feet  from  aUble.  1.) 

trnxsiLS  ANO  Mn.KiNa. 

Care  and  cleanliness  of  utensils  . 

Thoroughly  cleansed 5 

Inverted  In  pure  air 8 

Cleanliness  of  milking 

Clean,  dry  hands 8 

Udders  washed  and  dried  ..  6 
(Udders  cleaned  with  moist 
cloth,  4 ;  cleaned  with  dry  cloth 
at  least  IS  minutes  before  milk- 
ing. 1.) 

HANDUXO  THE  MtUC. 

Cleanliness  of  attendants 

llilk  removed  Immediately  from 
stable 

Cleanliness  of  milk  room 

Prompt  cooling.  (Cooled  imme- 
diately after  milking  each  cow) 

Efficient  cooling ;  below  SOP  ¥... 
(SI"  to  55°,  4;  56"  to  60<».  2.) 

Storage:  below  80°  F 

(51<^tO  56°,  2:  56°  to  60°.  1.) 

Transportation;  Iced 

(For  jacket  or  wet  blanket  al- 
low 2:  dry  blanket  or  covertrd 

wagon.  1.) 


Perfect.    Allowed. 


Score  for  equipment +  Score  for  methods = Final  score. 

NoTt  1.— If  any  filthy  condition  Is  found,  particularly  dirty  utensils,  the  total  score  shall  be  limited  to  49 
NoTC  2  —If  the  water  is  exposed  to  danserous  contamination  or  there  is  evidence  of  the  presence  o(  1 
dsngerous  disease  In  animals  or  attendants,  the  score  shall  be  0. 


26  QUESTIONS   AND  ANSWERS 

How   does   the  fat   affect   the   specific  gravity  of 
milk? 
The  specific  gravity  of  milk  fat  being  only  a  little 
more  than  .9,  it  is  lighter  than  the  other  constituents 
and  tends  to  lower  the  specific  gravity. 

Why  is  it  that  milks,  naturally  rich  in  fat,  have  a 

higher   specific    gravity    than    milks    naturally 

poor  in  fat? 

Pure  milks,  rich  in  fat,  contain  larger  percentages 

of  solids  not  fat  than  do  those  of  low  fat  content. 

Take,  for  example,  samples  of  milk  of  the  following 

composition : 

Board  of  health 
Fat  Solids  not  fat     lactometer  reading 

I 3.9  8.6  108. 

2 4.9  9.1  III. 

No.  2  contains  i  per  cent  more  fat  and  .5  of 
I  per  cent  more  solids  not  fat  than  does  No.  i. 
One  per  cent  of  fat  lowers  the  lactometer  read- 
ing practically  3  degrees,  while  .5  of  i  per  cent 
of  solids  not  fat  raises  the  lactometer  at  least  6 
degrees.  Thus  we  have  a  final  lactometer  reading 
of  III  in  the  richer  milk. 

What  is  the  specific  gravity  of  the  milk  solids? 

The  solids  of  normal  milk  have  a  specific  gravity 
between  1.25  and  1.34,  the  average  being  about 
1.30. 

What  is  the  specific  gravity  of  the  solids  not  fat? 

The  solids  not  fat  are  made  up  of  casein,  albumin, 
sugar,  and  mineral  matter,  and  have  a  specific 
gravity  of  about  1.50. 


ON    MILK  AND   MILK-TESTING  2/ 

What  is  the  specific  gravity  of  milk  protein? 

It  is  held  by  some  that  the  specific  gravity  of 
milk  protein  is  about  1.34. 

How  does  milk  fresh  from  the  cow  differ  in  specific 
gravity  from  milk  several  hpurs  old? 
Fresh  milk  has  a  lower  specific  gravity,  due  in  all 
probability  to  the  gases  in  the  fresh  milk.  For  this 
reason  milk  should  be  several  hours  old  when  tested 
if  accurate  results  are  desired. 

What  is  a  lactometer? 

It  is  a  form  of  hydrometer  made  especially  for 
taking  the  specific  gravity  of  milk. 

What   two  forms   of  lactometers   are  in  common 
use? 

The  Quevenne  lactometer  and  the  New  York 
board  of  health  lactometer. 

Describe  a  Quevenne  lactometer. 

It  consists  of  a  hollow,  cylindrical  body  so 
weighted  at  one  end  that  when  floated  in  milk  it 
takes  an  upright  position.  A  stem  is  attached  to 
the  upper  end  of  the  body.  The  stem  contains  a 
scale  so  graduated  and  set  that  when  the  instru- 
ment is  floated  in  the  milk  the  specific  gravity  may 
be  read  at  the  upper  surface  of  the  liquid.  The 
better  class  of  instruments  contain  a  thermometer, 
the  bulb  being  melted  in  the  lower  end  of  the  body 
and  the  scale  appearing  directly  over  the  lactometer 
scale. 


28  QUESTIONS   AND  ANSWERS 

Describe  the  Quevenne  lactometer  scale. 

The  scale  is  graduated  from  15  to  40,  each  gradu- 
ation marking  one  lactometer  degree,  and  figures 
denote  the  reading  every  five  degrees.  When  the 
floating  instrument  comes  to  rest  with  the  surface 
of  the  liquid  on  the  15  mark  the  liquid  has  a  specific 
gravity  of  1.015,  and  when  it  comes  to  rest  in  a 
liquid  with  the  surface  on  the  40  mark  the  liquid 
has  a  specific  gravity  of  1.040.  Hence  to  obtain 
the  specific  gravity  place  the  figures  i.o  in  front  of 
the  lactometer  readings. 

At  what  temperature  should  the  lactometer  read- 
ing be  taken? 
The  lactometers  are  made  to  be  used  at  60°  F. 

If  the  milk  is  at  a  temperature  above  or  below 
60°  F.,  can  a  correction  be  made  on  the 
Quevenne  lactometer  reading? 

When  the  temperature  of  the  milk  is  between 
60°  F.  and  70°  F.,  add  .1  to  the  lactometer  reading 
for  each  degree  above  60.  When  the  temperature 
of  the  milk  is  below  60  and  above  50  subtract  .1 
from  the  lactometer  reading  for  each  degree  below 
60.  This  correction  is  only  approximate  and  can- 
not be  used  for  wider  variations  in  temperature 
than  those  given  above.  The  temperature  of  milk 
should  be  brought  within  those  limits  before  tak- 
ing the  lactometer  reading. 

Describe  the  New  York  board  of  health  lactometer. 

It  has  the  general  appearance  and  form  of,  and 
is  made  like,  the  Quevenne  lactometer,  but  the 
graduations  on  the  scale  are  dififerent. 


ON    MILK  AND   MILK-TESTING  29 

Describe  the  graduations  on  the  scale  of  a  board  of 
health  lactometer. 
The  scale  extends  from  zero  to  120.  The  zero 
point  is  at  the  top  of  the  stem  at  the  mark  to 
which  the  lactometer  sinks  in  water  at  60°  F. 
When  the  instrument  is  floated  in  cleanly  skimmed 
milk  the  surface  of  the  liquid  would  be  near  the 
120  mark;  100  marks  the  point  below  which  the 
instrument  is  never  expected  to  settle  in  pure  milk. 
There  are  60  divisions  on  the  scale,  each  division 
equaling  two  lactometer  degrees. 

What  is  the  temperature  correction  for  the  board 
of  health  lactometer? 
Add  .3  to  the  lactometer  reading  for  each  degree 
of  temperature  above  60°  F.,  and  subtract  .3  for 
each  degree  below  60°  F.  If  the  temperature  of 
the  milk  is  more  than  10  degrees  from  60  degrees, 
bring  it  within  those  limits  before  taking  the  read- 
ing, as  the  correction  cannot  be  used  for  greater 
variations  in  temperature. 

Compare   the  scales   on  the  board  of  health  and 
Quevenne  lactometers. 

The  zero  point  on  each  is  the  point  to  which  the 
instruments  sink  when  placed  in  water  at  60°  F. 
The  29  mark  on  the  Quevenne  scale  corresponds 
to  the  100  mark  on  the  board  of  health  scale,  hence 
each  board  of  health  lactometer  degree  is  .29  of  a 
Quevenne  lactometer  degree,  or  the  latter  is  344+ 
times  greater  than  the  former. 

How  may  one  lactometer  reading  be  converted  to 
that  of  the  other? 


30  QUESTIONS   AND  ANSWERS 

To  convert  the  board  of  health  lactometer  reading 
to  the  Quevenne  reading,  multiply  the  board  of 
health  reading  by  .29;  and  to  convert  the 
Quevenne  reading  to  board  of  health,  divide  the 
Quevenne  reading  by  .29. 

If  a  sample  of  milk  read  108  on  the  board  of  health 
lactometer  at  66°  F.,  what  would  its  specific 
gravity  be  at  60°  F.? 

In  this  problem  the  temperature  correction  may 
be  made  first,  then  convert  to  the  Quevenne  reading 
by  multiplying  by  .29,  and  finally  prefix  the  figures 
i.o. 

66—60=6.    6X.3=i.8. 

108+1.8=109.8. 

i09.8X.29=3i.84. 

The  specific  gravity,  therefore,  is  1.03 184. 

Between  what  graduations  on  the  board  of  health 
lactometer  may  normal  milks  vary? 
Between  103  and  115  and  in  some  few  cases  milk 
may  read  as  low  as  100  or  as  high  as  118. 

Between  what  graduations  on  the  Quevenne  lacto- 
meter may  normal  milks  vary? 
Between  30  and  34,  but  in  rare  cases  the  milk  may 
read  as  low  as  29  or  as  high  as  35. 

Upon  what  law  of  physics  does  the  action  of  the 
lactometer  depend? 
It  depends  upon  the  fact  that  a  solid  body  float- 
ing  in   a   liquid   displaces   a   weight   of   the   liquid 
equaling  the  weight  of  the  floating  body. 


ON   MILK  AND   MILK-TESTING  3I 

How  should  the  lactometer  reading  be  made? 

It  may  be  conveniently  made  by  placing  the  milk 
in  a  cylinder,  15^  inches  in  diameter  and  10  inches 
high,  then  lowering  the  lactometer  in  the  milk  until 
it  floats.  Let  the  lactometer  adjust  itself  for  about 
half  a  minute  before  taking  the  reading.  If  more 
than  half  a  minute  elapses  before  taking  the  read- 
ing, cream  may  rise  and  affect  the  result. 

How  does  the  temperature  affect  the  specific  gravity 
of  milk? 
Heat  causes  milk  to  expand.     A  given  volume  of 
cold  milk  will  occupy  more  space  when  warmed  up. 
Hence,  heat  reduces  the  specific  gravity  of  milk. 

By  making  use  of  the  differences  in  specific  gravity 
of  its  constituents  can  one  test  milk  accurately 
for  its  fat  content  without  using  a  chemical? 
No,  because  some  of  the  milk  serum  will  rise 
with  the  fat,  even  when  great  centrifugal  force  is 
used  to  separate  them,  and  the  quantity  of  serum 
remaining  with  the  fat  will  vary  with  milks  of  dif- 
ferent quality. 

What  is  a  lactoscope,  and  how  is  it  used? 

It  is  an  instrument  for  determining  approximately 
the  amount  of  fat  in  milk.  It  may  be  of  some  value 
when  used  in  connection  with  the  lactometer.  The 
instrument  consists  of  a  graduated  glass  barrel  with 
a  tightly  fitting  stopper  at  the  bottom.  The  stopper 
carries  a  white  glass  cylinder  with  black  lines 
thereon.  The  cylinder  extends  up  into  the  barrel 
a  short  distance.  Four  c.  c.  of  milk  are  run  into 
the  barrel  and  water  added  with  thorough  mixing. 


32  QUESTIONS   AND  ANSWERS 

until  the  operator  can  distinguish  the  dark  lines  on 
the  cylinder  through  the  liquid.  The  graduations 
at  the  surface  of  the  liquid  in  the  barrel  then  in- 
dicate the  percentage  of  fat  in  the  milk. 

What  is  a  pioscope? 

It  is  an  instrument  for  determining  roughly  the 
quantity  of  fat  in  milk  or  whether  the  milk  is  of  a 
high  or  low  grade.  It  consists  of  a  shallow  recep- 
tacle with  a  rim  raised  slightly  above  a  surround- 
ing hard,  black  disk.  Into  the  receptacle  a  few 
drops  of  milk  are  placed  and  covered  with  a  cir- 
cular cover-glass  having  variously  tinted  seg- 
ments. The  milk  spreads  out  in  a  thin  layer  and 
its  color  as  seen  against  the  dark  background  may 
be  matched  by  one  of  the  tinted  glass  segments. 
The  different  tinted  segments  represent  different 
grades  of  milk. 

Describe  in  brief  the  Babcock  test. 

The  test  was  perfected  by  Professor  Babcock  and 
given  to  the  public  in  1890.  It  depends  upon  sul- 
phuric acid  to  free  the  fat-globules  and  upon  cen- 
trifugal force  to  bring  the  fat  together  so  that  it 
may  be  measured.  A  definite  quantity  of  the  milk 
is  placed  in  a  glass  bottle,  sulphuric  acid  is  added, 
the  mixture  well  shaken,  then  placed  in  a  centrif- 
ugal machine  and  whirled  to  bring  the  fat  to- 
gether. Water  is  then  added  to  the  bottles  ur.til 
the  fat  rises  in  the  graduated  part  of  the  neck, 
where  the  volume  of  the  melted  fat  can  be  read 
directly  in  percentage. 


ON   MILK  AND   MILK-TESTING  33 

Describe  the  Babcock  test  machine. 

•  Various  styles  are  found  on  the  market  made  to  be 
run  by  hand,  steam,  or  electrical  power.  They  vary 
in  size  from  the  small  two-  or  four-bottle  tester, 
convenient  to  carry  from  place  to  place,  to  the 
larger  machines  accommodating  24  or  more  bottles, 
and  suitable  for  f actory~  work.  They  usually  con- 
sist of  an  inclosing  frame  or  covering  and  a  hori- 
zontal revolving  disk  attached  to  a  shaft  in  the  cen- 
ter. Swinging  pockets  for  holding  test  bottles  are 
attached  to  the  rim  of  the  disk  in  such  a  way  that 
they  hold  the  bottles  upright  when  the  disk  is  quiet, 
but  in  a  horizontal  position,  with  the  opening 
toward  the  center,  when  the  disk  is  revolving.  In 
steam  machines  a  turbine  is  attached,  either  to  the 
upper  or  lower  end  of  the  shaft.  These  machines 
are  very  satisfactory  for  factory  work  where  steam 
power  can  be  used,  while  the  hand  machines  are 
more  suitable  for  testing  small  dairies  or  where  a 
few  tests  are  made  occasionally. 

How  can  one  determine  the  number  of  revolutions 
the  disk  makes  for  one  revolution  of  the  handle 
in  a  hand  machine? 
Mark  a  point  on  the  rim  of  the  disk  and  turn  the 

handle  slowly  once  around,  counting  the  number 

of  times  the  point  on  the  disk  reaches  the  point  at 

which  it  started. 

How  many  revolutions  per  minute  should  the  disk 
in  a  Babcock  machine  make  in  order  to  do  good 
work? 

The  number  of  revolutions  depends  upon  the 
diameter  of  the  circle  in  which  the  bottles  whirl. 


34  QUESTIONS   AND  ANSWERS 

Farrington  and  Woll  have  figured  out  that  the  num- 
ber of  revolutions  should  be  those  given  in  the  fol- 
lowing table : 

Diameter  of  Revolutions 

the  disk  per  minute 

10" 1,074 

12'' 980 

14" 909 

16", 848 

18'' 800 

20'' 759 

22" 724 

24" 693 

What  conveniences  should  be  attached  to  a  Bab- 
cock  tester  run  by  steam? 

1.  Steam  gauge. 

2.  Steam  brake  for  stopping  the  disk. 

3.  Speed  indicator. 

4.  Water  heater  and  means  of  filling  bottles 
quickly. 

What   points   should   be   observed  in   selecting   a 
machine? 

1.  The  machine  should  be  durable  and  safe  to 
operate. 

2.  Should  run  smoothly. 

3.  Should  have  a  capacity  corresponding  to  the 
work  and  carry  an  even  number  of  bottles. 

4.  Pockets  should  always  swing  free  so  the 
bottles  may  come  to  an  upright  position  when  the 
disk  comes  to  rest. 

5.  The  bottles  should  be  protected  against  the 
entrance  of  oil  from  the  machine. 


ON    MILK  AND   MILK-TESTING  35 

6.  There  should  be  means  of  ventilation  for 
temperature  control. 

7.  Bearings  should  be  so  placed  that  heat  from 
the  steam  will  not  affect  them. 

8.  Means  should  be  provided  for  using  a  heavy- 
oil  where  the  bearings  may  become  heated  from 
the  steam. 

9.  The  bearings  should  be  protected  so  that 
acid  cannot  come  in  contact  with  them  when  bot- 
tles break  in  the  machine. 

How  should  the  milk  test  bottles  be  constructed? 

1.  The  graduated  portion  of  the  neck  should  be 
accurate. 

2.  The  bottles  should  hold  about  50  c.  c.  and  be 
made  of  tough  glass  of  even  thickness  throughout, 
and  strong  enough  to  stand  pressure  and  sudden 
changes  of  temperature. 

3.  The  top  of  the  body  of  the  bottle  should 
slant  toward  its  center  at  an  angle  not  greater  than 
40  degrees,  so  that  all  the  fat  may  rise  in  the  neck. 

4.  The  bottom  should  be  perfectly  flat,  so  that 
all  points  will  be  supported  evenly  while  being 
whirled  in  the  machine. 

5.  The  diameter  of  the  neck  should  be  neither 
too  large  nor  too  small,  and  should  be  the  same  as 
other  bottles  in  the  set  used. 

6.  The  top  should  be  strong,  well  annealed,  and 
flaring,  to  readily  admit  the  pipette  and  assist  in 
preventing  loss  when  milk  is  introduced. 

How  is  the  scale  on  the  neck  of  the  bottle  divided? 

Each  cubic  centimeter  of  space   is  divided  into 

five  equal  parts,   each   part   equaling  i    per   cent. 


36  QUESTIONS  AND  ANSWERS 

The  latter  are  divided  into  five  equal  parts,  each 
part  equaling  two-tenths  of  i  per  cent.  With  a 
little  practice*  one  may  read  accurately  to  one-tenth 
of  I  per  cent. 

Why  does  the  scale  on  the  neck  of  the  bottle  show 
the  per  cent  of  fat? 
Because  the  graduated  portion  holds  two  cubic 
centimeters  and  the  specific  gravity  of  melted  but- 
ter at  140°  F.  is  .9.  One  c.  c.  weighs  0.9  of  a  gram 
and  2  c.  c.  weigh  1.8  grams,  which  is  10  per  cent 
of  18  grams,  the  weight  of  milk  taken. 

What  can  be  done  to  make  the  scale  easy  to  read? 
Rub  it  over  with  a  soft  pencil,  burnt  cork  or  a 
paste  made  by  dissolving  asphalt  in  turpentine. 

How  may  the  test  bottles  be  marked  for  identifica- 
tion? 

1.  A  ground  space  may  be  made  on  the  body  or 
neck  of  the  bottle  upon  which  numbers  can  be 
placed  with  a  lead  pencil. 

2.  Copper  bands  with  stamped  numbers  can 
surround  the  neck  of  the  bottle. 

Describe  a  skim-milk  test  bottle. 

This  has  two  necks,  one  having  a  larger  bore. 
Substances  are  introduced  through  the  larger  bore, 
and  the  smaller  one,  which  is  graduated,  is  used  to 
collect  the  fat. 

When  placing  the  bottle  in  a  centrifuge,  the  large 
neck  should  be  turned  toward  the  center  of  the 
machine. 


ON   MILK  AND  MILK-TESTING  37 

What  points  in  the  construction  of  skim-milk  bot- 
tles need  special  attention? 

1.  The  scale  should  be  correct  and  the  bore  large 
enough  to  admit  milk  or  water  freely. 

2.  The  glass  should  be  tough  and  strong  enough 
to  stand  the  pressure  of  whirling  and  the  changes 
of  temperature. 

3.  The  top  of  the  body  should  slant  gradually 
toward  the  center,  with  no  uneven  places  where  fat 
might  collect. 

4.  The  large  neck  should  enter  the  body  at  the 
base  of  the  graduated  tube  and  extend  down 
through  the  center  of  the  body  almost  to  the  bot- 
tom so  that  the  acid  will  run  under  the  milk  and 
not  char  part  of  it  before  they  can  be  properly 
mixed. 

How  closely  can  percentage  be  read  on  a  skim-milk 
bottle? 

Some  bottles  are  graduated  to  measure  .01  per 
cent  while  others  read  only  as  low  as  .05  per  cent. 
On  either  form  one  can  distinguish  easily  varia- 
tions of  .01  per  cent. 

Describe  the  different  forms  of  Babcock  cream  test 
bottles. 

1.  Bottles  with  necks  having  a  graduated 
capacity  from  zero  to  30  of  40  per  cent  and  a  body 
so  large  that  an  18-gram  quantity  may  be  used, 
the  graduations  reading  to  i  per  cent  or  five-tenths 
of  I  per  cent. 

2.  Bulb-neck  bottles  of  the  same  capacity  as 
those  above,  but  graduations  reading  to  two-tenths 
of  I  per  cent. 


38  QUESTIONS   AND  ANSWERS 

3.  Bottles  with  capacity  of  9  grams  of  cream 
and  9  c.  c.  of  acid  and  a  scale  showing  the  percent- 
age direct  as  high  as  50  per  cent. 

4.  Bottles  with  scales  showing  the  percentage 
direct,  to  50  per  cent  for  9-gram  samples,  and 
with  bodies  large  enough  so  the  cream  may  be 
diluted  with  water  before  adding  the  acid. 

What  advantages  has  a  g-gram  cream  bottle 
over  other  forms  when  the  graduations  on  it 
show  the  percentage  direct  and  its  body  holds 
about  50  c.  c? 

1.  Accuracy  is  increased,  because  a  neck  of 
smaller  diameter  and  a  finer  scale  may  be  used. 

2.  In  reading  the  percentage  direct  any  error 
is  not  doubled  as  occurs  with  the  ordinary  bottle 
when  the  sample  is  divided  and  the  observed  read- 
ing is  doubled. 

3.  The  smaller  diameter  of  the  neck  reduces 
the  error  due  to  the  difficulty  of  making  proper 
allowance  for  the  space  occupied  by  the  meniscus. 

4.  The  size  of  the  body  allows  the  addition  of 
9  c.  c.  of  water  before  adding  the  usual  amount 
of  acid,  thus  diluting  the  cream  and  preventing  the 
acid  from  attacking  the  fat,  as  often  occurs  when 
equal  volumes  of  rich  cream  and  acid  are  mixed. 

5.  Richer  cream  may  be  tested,  as  the  bottle 
may  be  graduated  to  give  readings  of  50  per  cent. 

How  does  the  graduated  portion  of  the  neck  in 
cream  test  bottles  vary? 
I.     It    varies    in    capacity,    some    bottles    being 
graduated  from  zero  to  50  per  cent  and  others  from 
zero  to  30  per  cent,  etc. 


ON   MILK  AND   MILK-TESTING  39 

2.  It  varies  in  per  cent  represented  by  the 
smallest  divisions  on  the  scale,  which,  in  some 
bottles,  are  equal  to  i  per  cent,  while  in  others  they 
represent  two-tenths  of  i  per  cent. 

3.  When  a  cream  bottle  is  made  with  a  bulb  in 
the  neck,  the  bulb  usually  represents  10  per  cent, 
and  is  not  otherwise  graduated.  The  graduated 
portion  above  and  below  the  bulb  may  be  graduated 
as  fine  as  two-tenths  of  i  per  cent. 

What  should  be  the  capacity  of  cream  test  bottles? 
The  part  below  the  neck  should  hold  about  50 
c.  c,  even  though  only  9  grams  of  cream  are  used 
in  making  the  test. 

How  should  the  pipette  be  made? 

1.  Of  tough  glass  with  a  strong  annealed  tip, 
and  having  an  opening  large  enough  to  allow  the 
milk  to  run  out  freely,  yet  not  so  large  as  to  flood 
the  neck  of  the  test  bottle. 

2.  The  tube  below  the  body  should  be  about 
4  inches  long,  and  small  enough  to  enter  the  neck 
of  the  bottle. 

3.  The  space  between  the  upper  end  of  the 
pipette  and  the  mark  on  the  stem  should  be  large 
enough  so  that  after  filling  the  pipette,  one  will 
have  time  to  place  the  finger  over  the  end  before 
the  milk  runs  below  the  mark. 

How  much  milk  should  the  pipette  deliver? 

It  should  deliver  18  grams  of  milk,  or  17.44  c.  c 
18-7-1.032  (sp.  g.  milk)=i7.44. 


40  QUESTIONS   AND  ANSWERS 

Why  is  the  pipette  marked  17.6? 

Because  it  holds  17.6  c.  c.  Some  milk  is  always 
left  in  the  pipette,  and  this  makes  up  the  difference 
between  17.6  and  17.44. 

What  is  meant  by  *' calibrating "   Babcock  glass- 
ware? 

It  means  the  determination  of  the  correctness  of 
the  graduations  on  the  glassware. 

By  what  methods  can  glassware  be  calibrated? 

1.  By  the  use  of  a  plunger 

2.  By  the  use  of  a  scale. 

3.  By  the  use  of  mercury. 

4.  By  the  use  of  an  accurate  pipette  or  burette. 

Describe  how  milk-testing  bottles  may  be  calibrated 
by  the  use  of  a  plunger. 

The  bottle  is  filled  to  the  zero  mark  with  some 
liquid  such  as  water.  Any  drops  of  the  liquid 
clinging  to  the  walls  of  the  neck  above  the  zero 
mark  should  be  removed  with  a  strip  of  blotting 
paper.  A  brass  plunger  divided  into  two  sections 
connected  by  a  small  wire,  and  each  section  equal- 
ing I  c.  c,  is  inserted  in  the  neck  of  the  bottle  until 
the  first  section  is  completely  submerged.  The 
level  of  the  liquid  should  then  be  exactly  on  the 
5  per  cent  mark. 

The  plunger  is  then  inserted  farther  into  the 
bottle  until  the  second  section  is  submerged,  when 
the  surface  of  the  liquid  should  reach  the  10  per 
cent  mark,  if  the  bottle  is  correctly  graduated. 
Bottles  showing* a  variation  of  more  than  .2  per 
cent  should  be  rejected. 


ON    MILK  AND   MILK-TESTING  4I 

How  may  cream-testing  bottles  be  calibrated  by 
the  use  of  a  plunger? 

In  the  same  manner  as  milk-testing  bottles,  ex- 
cepting thSt  a  larger  plunger  is  used.  Each  c.  c. 
of  space  occupied  by  the  plunger  equals  5  per  cent 
in  the  neck  of  the  bottle. 


What  precautions  should  be  taken  in  calibrating 
with  a  plunger? 

1.  Have  the  surface  of  the  liquid  level  with  the 
zero  mark. 

2.  Remove  any  liquid  adhering  to  the  walls  of 
the  neck  above  zero  mark. 

3.  The  plunger  should  be  dry  before  inserting. 

4.  There  should  be  no  air  bubbles  in  the  neck 
during  calibration. 

5.  The  temperature  of  the  plunger  should  be  the 
same  as  that  of  the  liquid. 

6.  While  calibrating  do  not  allow  heat  from  the 
hand  to  cause  the  liquid  to  expand. 

How  may  testing  bottles  be  calibrated  by  use  of 
scales  ? 

Fill  the  bottle  to  the  zero  mark  with  water  and 
balance  it  on  the  scales.  Add  i  gram  of  water.  The 
surface  of  the  liquid  should  then  be  exactly  on  the 
5  per  cent  mark.  On  addition  of  another  gram  of 
water  the  surface  should  be  level  with  the  10  per 
cent  mark.  Each  two-tenths  of  a  gram  equals  i 
per  cent  in  the  neck  of  the  bottle.  By  this  means 
any  part  of  the  neck  of  milk  or  cream  bottles  may 
be  calibrated. 


42  QUESTIONS  AND  ANSWERS 

How  may  mercury  be  used  to  calibrate  the  testing 
bottles? 

From  a  correctly  graduated  burette  run  2  c.  c.  of 
mercury  into  the  clean  and  dry  test  bottle.  Then 
push  a  close-fitting  stopper  into  the  neck  of  the 
bottle  level  with  the  highest  graduation.  When 
the  bottle  is  turned  upside  down  the  mercury  should 
just  fill  the  graduated  portion  of  the  neck.  The 
mercury  may  be  transferred  from  one  bottle  to  an- 
other without  loss  by  connecting  the  necks  with  a 
piece  of  closely  fitting  rubber  tubing.  In  this 
manner  several  bottles  may  be  tested  with  the 
same  mercury. 

How  may  the  bottles  be  calibrated  by  use  of  a 
burette? 

Fill  the  bottles  exactly  to  the  zero  mark  with  a 
liquid.  Then  run  in  from  the  burette  liquid  to  fill 
the  graduated  part  of  the  neck.  Each  two-tenths 
of  a  c.  c.  taken  from  the  burette  should  equal  i  per 
cent  in  the  neck  of  the  bottle.  By  this  means  each 
per  cent  of  space  in  the  neck  may  be  readily  cali- 
brated. 

How  may  the  pipette  be  calibrated? 

By  closing  the  tip  and  running  in  17.6  c.  c.  of 
liquid  from  a  correctly  graduated  burette.  The 
surface  of  the  liquid  should  then  be  level  with  the 
mark  on  the  stem.  Or  one  may  accurately  balance 
a  small  vessel  on  scales.  Place  18  grams  on  the 
opposite  side  of  the  scales.  Then  fill  the  pipette 
to  the  mark  with  milk  having  a  Quevenne  lac- 
tometer reading  of  32.  Allow  the  milk  to  run  into 
the  vessel,  blowing  the  drop  from  the  tip  of  the 


ON   MILK  AND   MILK-TESTING  43 

pipette  into  the  vessel.  The  quantity  of  milk  de- 
livered from  the  pipette  should  just  balance  the  18 
grams  placed  on  the  other  side  of  the  scales. 

How  may  the  acid  measure  be  calibrated? 

1.  By  running  into  the  measure  from  a  gradu- 
ated burette  17.5  c.  c.  water.  The  upper  surface 
should  then  just  reach  the  17.5  mark. 

2.  Balance  the  measure  on  a  scale  and  place  17.5 
grams  weight  on  the  opposite  side.  Then  fill  the 
measure  to  the  mark  with  water.  The  weight  of 
the  water  should  just  balance  the  17.5  gram  weight. 

What  forms  of  acid  measures  are  used? 

1.  A  glass  cylinder  holding  17.5  c.  c. 

2.  The  Swedish  acid  bottle  and  17.5  c.  c.  pipette 
combined. 

What  acid  is  used  in  the  Babcock  test? 

Sulphuric  acid,  with  a  specific  gravity  of  1.82  to 
1.83  and  strong  enough  to  produce  a  light  yellow 
color  in  fat. 

What  substances  other  than  acids  are  sometimes 
used? 
Solvents  like  ether,  alcohol,  or  petroleum  spirits 
may  be   used  to  bring  the   fat   into   solution   and 
separate  it  from  the  milk  serum. 

What  are  the  principal  reasons  for  using  an  acid  in 
testing  fat? 

I.  To  destroy  the  sugar  and  films  of  casein  that 
entangle  the  fat. 


44  QUESTIONS  AND  ANSWERS 

2.  To  destroy  the  viscosity  of  the  fluid  and  to 
free  the  fat-globules. 

What  should  be  the  color  of  the  sulphuric  acid? 

It  should  be  clear  and  almost  colorless.  Organic 
matter  falling  into  the  acid  becomes  charred  and 
darkens  the  color.  This  does  not  spoil  the  useful- 
ness of  the  acid,  unless  undissolved  particles  are 
present  which  would  spoil  readings. 

What  are  the  advantages  of  using  sulphuric  acid  in 
the  Babcock  test? 

1.  It  quickly  dis^lves  milk  solids  other  than 
fat  and  destroys  viscosity,  thus  liberating  the  fat. 

2.  In  combining  with  the  water  and  solids  of  the 
serum,  it  generates  much  heat,  which  melts  the  fat. 

3.  It  increases  the  specific  gravity  of  the  liquid 
surrounding  the.  fat,  thus  making  it  easy  for  the 
fat  to  separate. 

4.  It  IS  comparatively  cheap  and  easy  to  obtain. 

5.  It  is  non-volatile  when  hot,  and  so  produces 
no  injurious  gases. 

How  may  one  determine  if  the  acid  is  of  proper 
strength? 

By  using  a  form  of  hydrometer  called  an  acid- 
meter.  This  instrument,  when  placed  in  the  acid, 
should  come  to  rest  with  the  surface  of  the  liquid, 
between  the  graduations  1.82  and  1.83.  A  little 
experience  will  enable  one  to  judge  by  the  appear- 
ance of  the  fat  at  the  end  of  the  test  if  the  acid  is  of 
proper  strength. 


ON    MILK  AND   MILK-TESTING  45 

If  the  acid  is  too  strong,  how  may  it  be  corrected? 

1.  By  adding  the  acid  to  a  small  quantity  of 
water. 

2.  By  using  less  acid  in  testing. 

3.  By  cooling  both  milk  and  acid  before  mixing. 

If  the  acid  is  too  weak,  how  may  it  be  corrected? 

1.  By  using  a  larger  quantity. 

2.  By  warming  both  acid  and  milk  before  test- 
ing. 

3.  If  ^rnuch  too  weak,  the  acid  should  be  dis- 
carded. 

Will  the  acid  weaken  with  age? 

Not  if  kept  in  tightly  stoppered  containers.  It 
will,  however,  absorb  water  from  the  air  and  be- 
come weaker  if  left  in  open  vessels. 

Why   is   it   that   acid   which   was    of   the    proper 
strength    in    winter    will    be    apparently    too 
strong  in  summer? 
During  summer  the  acid,  milk  and  apparatus  has 

a  higher  temperature,  so  the  acid  appears  stronger. 

The  remedy  is  to  cool  both  acid  and  milk. 

What  kind  of  stoppers  should  be  used  in  bottles 
containing  sulphuric  acid? 
Glass    stoppers   only.     The   acid   and    its    fumes 
destroy  both  cork  and  rubber. 

How  may  red  spots,  produced  on  clothing  by  acid, 
be  removed? 

If  the  acid  has  not  been  in  contact  with  clothing 


46  QUESTIONS   AND  ANSWERS 

too  long,  an  application  of  dilute  ammonia  will  re- 
move the  spots. 

What  precautions  are  necessary  in  handling  sul- 
phuric acid? 

1.  All  vessels  containing  acid  should  be  plainly 
marked. 

2.  It  should  be  kept  in  tightly  stoppered  glass 
bottles. 

3.  Tables,  sinks,  drains,  and  pipes  which  come- 
in  contact  with  acid  should  be  covered  with  lead. 

4.  In  mixing,  always  add  the  acid  to  the  other 
liquid — not  the  liquid  to  the  acid. 

5.  In  measuring  or  pouring,  keep  acid  away  from 
the  face. 

6.  If  a  bottle  breaks  in  the  centrifuge,  flush  the 
machine  with  plenty  of  cold  water. 

7  If  acid  is  spilled  it  should  be  cleaned  up  with 
a  cloth  immediately  and  the  spot  covered  with  a 
strong  alkali. 

8.  If  acid  is  spilled  on  the  flesh,  wash  it  off  im- 
mediately with  cold  water  and  apply  lime  water 
or  some  dilute  alkali. 

9.  Refuse  material  containing  acid  should  be 
disposed  of  where  it  will  not  come  in  contact  with 
valuable  vegetation,  animals,  or  persons. 

What  kinds  of  milk  may  be  tested  with  the  Bab- 
cock  test? 
All    kinds    from   which    a    fair    sample    may   be 
secured. 

Can  a  person  who  has  had  no  chemical  training  use 
a  Babcock  test? 


ON    MILK  AND   MILK-TESTING  47 

Yes,  anyone  capable  of  following  directions  and 
who  will  exercise  proper  care  may  learn  in  a  short 
time  to  use  the  test  correctly. 

How   should   the   milk   sample   be   taken   on    the 
weighing  stand? 

The  sample  is  best  secured  by  using  a  sampling 
tube,  because  it  takes  the  same  proportionate 
amount  from  each  quantity  sampled  and  takes  a 
uniform  column  from  the  upper  surface  to  the 
bottom  of  the  milk.  When  the  quantity  and  qual- 
ity of  the  milk  varies  but  little  from  day  to  day,  it 
may  be  sampled  with  a  small  dipper  with  good 
results.  A  graduated  glass  tube  can  be  used  by 
taking  lo  or  20  c.  c.  for  each  100  pounds  of  milk, 
or  I  c.  c.  for  each  pound  when  sampling  milk  from 
individual  cows.  The  sample  of  a  patron's  milk 
at  a  receiving  station  should  be  taken  immediately 
after  it  has  been  poured  into  the  weighing  can.  It 
should  be  transferred  at  once  to  the  proper  con- 
tainer. Several  forms  of  milk  samplers  or  milk 
thieves  are  on  the  market  and  most  of  them  give 
good  results  with  milk. 

How  much  milk  should  be  taken  for  a  sample? 

Enough  so  that  in  case  of  an  accident  occurring 
during  the  first  test  you  would  still  have  some  left 
to  make  another.     About  6  ounces  is  .sufficient. 

When  the  value  of  a  patron's  milk  is  determined  by 
its  fat  content,  how  often  should  the  milk  be 
sampled  ? 
Each  quantity  weighed  in  should  be  sampled  and 

tested  either  by  itself  or  by  a  composite. 


48  QUESTIONS  AND  ANSWERS 

"What  is  a  composite  sample,  and  why  are  such 
samples  used? 
A  composite  sample  is  the  quantity  of  milk  se- 
cured by  mixing  together  samples  of  different  days* 
milk.  They  are  taken  in  order  to  determine  in  one 
test  the  average  amount  of  fat  in  the  milk  received 
for  a  definite  period  at  different  times. 

How  should  composite  samples  be  kept? 

In  airtight  bottles  in  a  cool,  dark  place  conven- 
ient to  the  place  where  milk  is  weighed  and 
sampled.  They  should  be  kept  under  lock  and 
key,  and  sufficient  preservative  should  be  added  to 
keep  the  milk  in  good  condition  until  tested. 

What  points  should  be  considered  when  securing 
containers  for  composite  samples? 

1.  They  should  be  durable  and  easy  to  clean. 

2.  Stoppers  should  fit  tightly  and  be  easily  re- 
moved. 

3.  They  should  have  large  necks  so  that  milk 
may  be  added  to  or  taken  from  them  quickly  and 
without  loss. 

4.  They  should  be  of  convenient  size  and  prop- 
erly marked  to  identify  each  sample. 

What  preservatives  are  used  in  composite  samples? 

1.  Corrosive  sublimate  or  mercuric  chlorid. 

2.  Bichromate  of  potash. 

3.  Formaldehyde. 

What  are  the  advantages  of  corrosive  sublimate? 
I.     It  is  an  effective  preservative. 


ON   MILK  AND   MILK-TESTING  49 

2.  Small  quantities  are  used. 

3.  Can  be  secured  in  a  convenient  tablet  form. 

What  are  the  disadvantages  of  corrosive  sublimate? 

1.  It  is  a  deadly  poison. 

2.  In  excess  it  hardens  milk  casein  so  that  the 
acid  does  not  dissolve  it  so  readily. 

How  much  preservative  should  be  used? 

Enough  to  keep  milk  or  cream  sweet  until  tested. 
Usually  one  to  two  tablets  of  mercuric  chlorid  will 
preserve  one-half  pint  for  two  weeks.  Of  formalin 
one-half  c.  c.  should  preserve  the  same  sample  for 
two  weeks.  If  bichromate  of  potash  is  used,  add 
enough  of  it  to  give  the  milk  a  lemon-yellow  color. 
About  15  grains  is  usually  sufficient  to  keep  a  pint 
of  milk  for  two  weeks. 

What  are  the  advantages  of  formalin? 

1.  It  is  a  good  antiseptic. 

2.  It  is  in  liquid  form. 

3.  It  is  not  a  violent  poison. 

What  are  the  disadvantages  of  formalin? 

It  tends  to  harden  casein  so  that  sulphuric  acid 
does  not  readily  dissolve  it. 

What  are  the  qualities  of  potassium  bichromate  as 
a  preservative? 

1.  It  is  inexpensive. 

2.  It  is  not  a  violent  poison. 

3.  It  colors  the  milk  yellow  and  the  quantity 
necessary  to  add  can  be  determined  by  the  depth 
of  color  of  the  solution. 


50  QUESTIONS   AND  ANSWERS 

The  disadvantages  are: 

1.  Excessive  amounts  are  sometimes  necessary 
in  hot  weather  to  preserve  the  milk. 

2.  Then  it  interferes  with  the  acid  dissolving  the 
casein  and  a  clear  test  is  not  secured. 

3.  High  acidity  of  the  milk  reduces  its  preserva- 
tive qualities. 

4.  Samples  containing  it  may  form  a  tough  skin 
over  the  surface,  especially  in  the  light,  more  read- 
ily than  with  other  preservatives. 

How  should  the  composite  bottle  be  handled  while 
adding  milk? 
Each  time  a  bottle  is  taken  from  its  place  it 
should  be  held  in  an  upright  position  until  it  has 
been  quickly  whirled  in  a  circle.  This  mixes  the 
fat  with  the  remainder  of  the  sample  and  prevents 
it  from  becoming  attached  to  the  sides  of  the  bottle 
and  drying.  The  next  portion  of  milk  may  then 
be  added  and  the  Sample  shaken  once  more  to  dis- 
tribute the  fresh  milk  and  the  preservative  evenly. 

How  often  should  composite  samples  be  shaken, 
and  how  long  may  they  be  kept  before  testing? 
Composite  samples  should  be  shaken  once  a  day 
whether  fresh  milk  is  added  or  not.  They  should 
be  tested  every  ten  days  or  two  weeks  at  the 
longest. 

What  special  precautions  are  necessary  in  the  test- 
ing of  composite  samples? 
I.     Be  certain  that  any  cream  that  may  have  be- 
come attached  to  the  sides  of  the  container  is  re- 
moved. 


ON    MILK  AND   MILK-TESTIN  5 1 

2.  That  all  lumps  or  dried  particles  are  dissolved 
and  evenly  distributed.  This  may  be  accomplished 
by  warming  the  sample  not  higher  than  105°  to 
110°  F.  and  mixing.  Then,  if  necessary,  pass  the 
cream  through  a  fine  sieve  and  mix  before  drawing 
the  sample. 

3.  Take  extra  care  to  have  all  casein  dissolved, 
as  the  presence  of  a  preservative  makes  it  less 
soluble. 

What  special  points  should  be  observed  in  testing 
cream  ? 

1.  The  bottles  in  a  set  should  all  be.  of  the  same 
make. 

2.  They  should  be  graduated  to  two-tenths  of 
I  per  cent. 

3.  The  bottles  should  have  a  plain  distinguish- 
ing mark. 

4.  Secure  a  representative  sample  of  the  cream. 

5.  Use  the  same  quantity  of  cream  in  each  test. 

6.  Make  tests  in  duplicate. 

7.  Weigh  out  samples. on  balances  accurate  to 
Yio  of  a  gram. 

8.  Do  not  destroy  the  sample  until  the  results  of 
the  test  are  written  down. 

9.  The  volume  of  acid  used  should  be  the  same 
as  the  volume  of  substance  to  which  it  is  added. 

10.  Shake  the  bottles  for  some  time  after  the 
casein  is  all  dissolved. 

11.  Be  sure  the  temperature  of  the  fat  is  right  at 
the  time  of  reading. 

12.  Read  the  scale  from  the  bottom  of  the  fat 
column  to  the  bottom  of  the  meniscus. 


52  QUESTIONS    AND   ANSWERS 

13.  Write  down  results  immediately  upon  read- 
ing them. 

14.  If  tests  are  not  satisfactory  in  every  par- 
ticular, make  them  over.  Honest  results  cannot  be 
accomplished  without  accurate  work. 

How  would  you  proceed  to  secure  a  proper  sample 
of  the  milk  for  testing? 

Where  possible,  mix  the  milk  by  pouring  it  from 
one  vessel  to  another  two  or  three  times.  If  the 
cream  has  risen,  care  should  be  taken  so  that  it  is 
all  reincorporated  with  the  milk  and  evenly  dis- 
tributed. When  it  is  impossible  to  pour  the  milk, 
use  some  appropriate  instrument  to  thoroughly  stir 
it,  then  while  the  fat  is  evenly  distributed  the 
samples  must  be  taken,  using  a  17.6  c.  c.  pipette  or 
18  grams  weighed  on  a  scale. 

How  is  the  milk  transferred  to  the  test  bottle? 

By  sucking  it  up  into  a  pipette,  quickly  placing 
the  forefinger  over  the  end  and  allowing  the  milk 
to  escape  until  its  surface  is  level  with  the  17.6  c.  c. 
mark  on  the  stem.  Then  place  the  tip  of  the  pipette 
a  short  distance  into  the  neck  while  holding  the 
bottle  in  a  slanting  position,  so  that  its  opening  will 
not  be  entirely  closed.  By  reducing  the  pressure 
with  the  forefinger  the  milk  will  run  down  the 
side  of  the  neck  and  will  not  be  blown  out  by  es- 
caping air.  The  drop  remaining  in  the  tip  of  the 
pipette  should  be  blown  into  the  test  bottle. 

How  much  acid  is  used,  and  how  is  it  added? 

A  volume  of  sulphuric  acid  equal  to  the  volume 
of  milk  tested  is  used.     It  is  usually  measured  in  a 


ON    MILK  AND   MILK-TESTING  53 

small  cylinder  and  transferred  to  the  test  bottle, 
allowing  it  to  run  down  the  side  of  the  neck.  Any- 
adhering  milk  will  be  washed  down  if  the  bottle  is 
rotated  during  the  process.  The  acid  should  run 
under  the  milk  until  all  is  added.  Then  mix  it 
quickly  and  thoroughly  by  holding  the  bottle  in  a 
slanting  position  and  whirling  the  body  in  a  circle 
while  the  top  remains  stationary. 

When  should  the  test  bottles  be  whirled  in  the 
centrifuge? 

Immediately  upon  mixing  with  the  acid  and 
while  still  hot.  The  test  would  not  be  spoiled  if 
the  bottles  stood  for  a  time  before  whirling,  but  it 
would  be  necessary  to  heat  them  to  the  proper  tem- 
perature before  beginning  the  operation. 

How  long  and  how  often   should  the  bottles  be 
whirled? 

The  first  whirling  should  last  five  minutes. 
Water  is  then  added  until  the  fat  rises  to  the  base 
of  the  neck.  Then  whirl  for  two  minutes  to  wash 
the  fat  free  from  any  undissolved  substance.  Hot 
water  is  again  added  until  the  bottom  of  the  fat 
column  is  some  distance  above  the  zero  mark.  Then 
the  final  whirling  is  given  for  one  minute. 

How  should  the  water  be  added? 

Hot,  with  some  form  of  pointed  tube  or  pipette 
and  allowed  to  fall  directly  on  the  fat  to  wash  out 
undissolved  particles.  In  the  Mitchell-Walker  test 
the  water  enters  the  bottles  from  a  revolving  water 
centrifuge  while  the  machine  is  running. 


54  QUESTIONS   AND  ANSWERS 

What  character  of  water  should  be  used? 

Soft  water  should  be  used  when  possible,  but  any- 
ordinary  good  water  will  serve.  One  or  two  cubic 
centimeters  of  sulphuric  acid  added  to  the  water 
used  for  the  final  filling  will  aid  materially  in  giv- 
ing a  clear  fat  column,  especially  if  the  water  is 
hard. 

Why  does  the  mixture  of  milk  and  acid  become 
hot? 

Sulphuric  acid,  combining  with  the  water  of 
milk,  generates  most  of  the  heat.  Some  heat  is 
developed  by  the  action  of  the  acid  on  the  milk 
solids. 

Why  does  the  mixture  turn  dark? 

The  acid  burns  or  oxidizes  the  milk  solids,  which 
contain  carbon.  The  darkening  process  is  similar 
to  burnt  wood,  becoming  dark  when  burned  in  air. 

If  the  acid  does  not  completely  dissolve  the  casein 
in  composite  samples,  how  may  the  difficulty 
be  overcome? 

1.  Have  the  acid  and  milk  at  a  slightly  higher 
temperature  than  usual  at  the  time  of  mixing. 

2.  Use  a  larger  amount  of  acid  than  ordinarily. 

3.  Shake  the  samples  for  a  longer  time  than 
usual  before  placing  them  in  the  machines. 

If  the  temperature  of  the  fat  is  not  right  when 
through  whirling,  how  may  it  be  corrected? 

1.  If  too  hot,  allow  the  bottles  to  stand  a  short 
time  at  room  temperature. 

2.  If  too  cold,  place  the  bottles  in  hot  water. 


ON    MILK  AND   MILK-TESTING  55 

3.  All  bottles  should  be  placed  in  water  of  about 
140°  F.  after  removal  from  the  machine  if  accurate 
and  uniform  results  are  desired. 

How  should  the  fat  column  appear  when  the  test 
is  completed? 

It  should  be  a  light  golden  yellow  throughout  its 
length,  with  no  specks  or  particles  of  undissolved 
matter  near  its  base,  and  the  liquid  in  the  neck 
under  the  fat  should  be  as  transparent  as  the  air 
above  it,  thus  giving  the  fat  the  appearance  of 
resting  in  the  neck  without  support. 

If  the  column  of  fat  is  darkened  and  contains  black 
specks  or  black  substance  at  its  bas**  what  does 
it  indicate? 
It  indicates  one  or  more  of  the  following  condi- 
tions : 

1.  That  the  acid  is  too  strong. 

2.  That  the  temperature  of  the  milk  or  acid,  or 
both,  was  too  high. 

3.  That  too  much  acid  was  used. 

4.  Improper  mixing. 

If  the  fat  column  is  light  in  color,  containing  white 
specks  or  a  clouded  or  white  mass  at  the  base, 
what  does  it  indicate? 

It  indicates  one  or  more  of  the  following  condi- 
tions : 

1.  That  the  acid  is  too  weak. 

2.  That  not  enough  acid  was  used. 

3.  That  the  milk  and  acid  were  too  cold  at  the 
time  of  mixing. 


56  QUESTIONS   AND  ANSWERS 

If  the  fat  has  the  proper  color,  but  contains  undis- 
solved substance,  what  is  the  trouble? 

It  usually  indicates  insufficient  mixing  before 
placing  in  the  centrifuge,  but  may  possibly  be  due 
to  improper  water. 

When  should  the  per  cent  of  fat  be  read? 

Immediately  upon  completing  the  whirling,  if 
the  temperature  of  the  fat  is  correct.  The  fat 
solidifies  at  about  100°  F.,  and  the  temperature  of 
the  bottles  should  be  considerably  above  that  dur- 
ing the  whirling. 

How  should  the  fat  be  measured? 

By  holding  the  fat  column  on  a  level  with  the  eye 
and  counting  the  diyisions  on  the  scale  in  that  part 
of  the  neck  occupied  by  the  fat.  Give  credit 
for  all  the  fat  between  the  lowest  and  highest  points 
on  the  fat  column.  Each  division  on  the  scale 
usually  represents  two-tenths  of  i  per  cent,  but 
some  bottles  are  now  made  upon  which  each  divi- 
sion represents  one-tenth  of  i  per  cent. 

How  may  an  instrument  assist  in  measuring  the 
fat? 

By  using  some  form  of  dividers  and  fixing  the 
points  at  the  extreme  ends  of  the  fat  column.  Then 
change  the  position  until  one  point  rests  on  the  zero 
mark  and  the  other  on  the  scale  above.  The  inter- 
vening space  will  have  a  length  equal  to  that  of  the 
fat  column  and  the  per  cent  may  be  read  directly. 

Does  all  the  fat  rise  in  the  neck  of  the  bottle? 
It  has  been  found  by  comparing  the  results  with 


ON   MILK  AND   MILK-TESTING  57 

chemical  analysis  that  about  one-tenth  of  i  per 
cent  will  not  rise.  When  credit  is  given  for  the 
curved  spaces  that  are  not  occupied  by  fat  at  the 
ends  of  the  fat  column,  the  results  agree  closely 
with  chemical  analysis. 

How  should  skim  milk  be  tested  for  fat? 

In  the  same  manner  as  whole  milk,  excepting 
that  a  special  double-neck  test  bottle  is  used. 
About  I  to  1.5  c.  c.  extra  amount  of  sulphuric  acid 
is  used,  and  the  machine  should  whirl  the  bottles 
about  a  minute  longer  than  usual.  The  fat  per- 
centage is  read  on  the  graduated  part  of  the  small 
neck. 

How  are  buttermilk  and  whey  tested  for  fat? 

In  the  same  manner  as  skim  milk,  excepting 
that  it  is  not  necessary  to  use  more  than  17.5  c.  c. 
of  sulphuric  acid. 

How  should  cream  be  tested  for  fat? 

By  weighing  accurately  a  representative  sample 
of  the  cream  into  a  special  cream  test  bottle,  and 
then  following  the  method  used  for  testing  whole 
milk. 

How  may  a  proper  sample  of  cream  be  secured? 

By  pouring  the  cream  from  one  vessel  to  another 
and  having  all  lumps  of  dried  cream  thoroughly  dis- 
tributed and  reincorporated.  Then  take  the  sample 
with  a  sampling  tube,  or,  if  one  cannot  be  secured, 
use  a  dipper  to  transfer  the  cream  to  the  sample 
bottle. 


58  QUESTIONS   AND  ANSWERS 

How  may  cream  that  is  frozen  be  sampled? 

Samples  should  not  be  taken  until  the  cream  is 
thawed  and  properly  mixed. 

Can  sour  cream  be  accurately  sampled? 

If  it  were  absolutely  necessary,  approximate  re- 
sults might  be  secured  by  adding  solid  caustic  soda 
to  neutralize  the  acid  and  dissolve  the  casein,  then 
take  the  sample  after  properly  mixing. 

What  quantity  of  cream  should  be  used  in  the  test 
bottle? 

That  depends  upon  the  capacity  of  the  graduated 
neck  and  the  richness  of  the  cream.  If  the  neck 
were  graduated  from  zero  to  30  per  cent  and  the 
cream  tested  more  than  30  per  cent,  less  than  18 
grams  of  cream  would  have  to  be  used,  and  the  per 
cent  would  be  as  much  greater  than  the  observed 
reading  as  the  quantity  taken  was  smaller  than  18 
grams. 

How  should  cream  in  sample  bottles  be  prepared 
for  testing? 

If  the  cream  is  in  a  fluid  condition  it  may  be 
mixed  by  pouring  from  one  bottle  to  another  several 
times,  but  if  it  is  lumpy  and  thick,  or  has  dried  on 
the  bottle,  it  should  be  warmed  to  105°  F.,  then 
properly  mixed  and  sampled.  To  destroy  lumps, 
pass  it  through  a  fine  sieve,  then  mix  and  test 
Heating  above  105°  F.'  is  liable  to  separate  some 
fat  from  the  rest  of  the  cream. 

Why  should  the  cream  sample  be  weighed  rather 
than  measured? 


ON    MILK  AND   MILK-TESTING  59 

1.  Because  with  every  change  in  the  per  cent  of 
fat  in  cream  there  is  a  change  in  the  specific  gravity, 
so  that  a  pipette  that  would  hold  the  proper  amount 
of  cream  of  one  quality  would  not  hold  the  right 
amount  of  cream  of  another  quality. 

2.  Cream  is  viscous  and  a  variable  amount  re- 
mains in  the  pipette. 

3.  Air  bubbles  become  incorporated  during  the 
mixing  and  gases  from  fermentation  also  cause 
bubbles  which  are  retained  in  the  cream  on  account 
of  its  viscosity,  so  that  in  measuring  out  such 
cream  too  small  a  quantity  would  be  secured. 

How  should  the  per  cent  of  fat  be  read? 

By  counting  the  graduations  between  the  bottom 
of  the  fat  column  and  the  bottom  of  the  meniscus 
at  the  upper  surface  of  the  fat. 

Why  do  we  not  read  to  the  top  of  the  meniscus  as 
in  the  case  of  milk  bottles? 
Because  the  diameter  of  the  neck  is  greater  and 
the  space  occupied  by  the  meniscus  is  larger  in 
cream  bottles  and  is  altogether  too  large  a  quantity 
to  allow  for  the  fat  that  does  not  rise. 

When  the  whole  of  the  fat  column  has  the  clouded 
appearance  and  color  of  muddy  water,  how  may 
it  be  corrected? 

I.  It  may  be  corrected  by  shaking  the  mixture  of 
cream  and  acid  for  several  minutes  before  whirling, 
in  the  meantime  keeping  the  bottles  hot.  After 
the  whirling  is  completed  the  condition  of  the  test 
may  be  improved  by  allowing  the  fat  to  solidify. 


60  QUESTIONS    AND   ANSWERS 

Then   rehuat   and    whirl   for   a   short   time   in  the 
machine  before  reading. 

2.  In  filling  after  first  whirling  use  a  mixture  of 
equal  volumes  of  sulphuric  acid  and  water. 

How  often  should  the  test  bottles  be  washed? 

The  bottles  should  be  thoroughly  washed  after 
each  test,  not  only  to  remove  the  fat,  but  also  to 
remove  other  foreign  matter  that  would  become  too 
firmly  attached  to  remove  if  left  in  while  making 
several  tests. 

How  should  the  test  bottles  be  washed? 

1.  Shake  them  well  when  emptying. 

2.  Rinse  with  hot  water  containing  some  good 
washing  powder. 

3.  Rinse  thoroughly  with  plain  hot  water. 

What  can  be  done  to  hasten  the  washing  process? 

Special  devices  which  enable  the  operator  to 
handle  several  bottles  at  a  time  may  be  used. 
These  consist  of  racks  for  holding  bottles  securely, 
trays  for  submerging  large  numbers  of  bottles  in 
the  washing  solutions,  and  sprays  for  rinsing. 

How  may  unsweetened  condensed  milk  be  tested 
by  the  Babcock  method? 

Thoroughly  mix  the  sample  and  weigh  20  grams 
into  a  bottle  or  flask.  Add  40  c.  c.  of  water  and 
shake  until  thoroughly  mixed.  Test  in  duplicate, 
weighing  18  grams  into  a  milk  test  bottle  and  pro- 
ceed as  in  testing  milk.  Multiply  the  reading  of  the 
fat  by  three  to  obtain  the  per  cent. 


ON   MILK  AND   MILK-TESTING  6l 

How  may  the  fat  in  sweetened  condensed  milk  be 
determined  by  the  Babcock  test? 

The  method  devised  by  Farrington  is  practically 
as  follows: 

Dissolve  40  grams  of  the  condensed  milk  in  100 
c.  c.  of  water.  Measure  into  a  milk-testing  bottle 
a  Babcock  pipette  full  to  the  mark  of  this  sokition. 
Add  about  3  c.  c.  of  the  sulphuric  acid  used  in 
testing  milk  and  shake  the  mixture  vigorously. 
The  coagulated  casein  incloses  the  fat  and  they  are 
thrown  down  together  by  whirling  in  the  machine 
at  a  high  speed  and  a  temperature  of  200°  F.  The 
liquid  containing  much  of  the  sugar  is  carefully 
poured  off.  Ten  c.  c.  of  water  is  then  added  and 
the  mass  of  curd  is  broken  up  and  thoroughly 
shaken  with  the  water  to  remove  more  sugar ;  3  c.  c. 
of  acid  is  again  added  and  the  bottle  whirled  as 
before.  The  liquid  is  again  poured  off.  The  test 
is  now  completed  by  adding  10  c.  c.  of  water  and 
17.5  c.  c.  of  sulphuric  acid  and  proceeding  as  in  the 
fat  test  for  milk.  Multiply  the  fat  reading  by  3.2 
to  obtain  the  per  cent. 

C.  B.  Cochran  proposes  the  following  method  for 
fat  in  sweetened  condensed  milk: 

"  Weigh  out  25  g^ams  of  the  sample,  dissolve  in 
water  and  make  up  to  100  c.  c.  Transfer  6  c.  c.  to 
a  double  tube  milk  flask  provided  with  a  small  bore 
tube  graduated  to  give  percentage  of  fat  for  5  c.  c. 
of  milk.  Add  4  c.  c.  of  ether  and  4  c.  c.  acetic  acid 
(80  per  cent  or  more  absolute  acid).  Acetic  acid 
of  this  strength  will  dissolve  the  curd,  but  has  no 
effect  on  the  sugar.  Place  the  flask  in  a  vessel  of 
warm  water  and  heat  until  the  ether  is  expelled. 
A  layer  of  milk  fat  will  now  be  seen  floating  on  a 


62  QUESTIONS   AND  ANSWERS 

clear  and  colorless  liquid.  Fill  the  flask  with  hot 
water,  thus  raising  the  fat  into  the  graduated  tube. 
The  percentage  of  fat  can  now  be  read.  The  sam- 
ple is  then  whirled  in  a  centrifugal  machine  and 
another  reading  made.  Multiply  the  reading  by- 
four." 

Why  is  it  impossible  to  test  sweetened  condensed 
milk  by  the  Babcock  method  in  the  ordinary 
way? 

Because  the  acid  chars  the  cane  sugar  and  does 
not  dissolve  all  of  it.  The  blackened  and  undis- 
solved sugar  rises  with  the  fat  and  makes  it  impos- 
sible to  secure  a  clear  reading. 

How  may  the  fat  content  of  dried  milk  or  milk 
powder  be  determined? 

Van  Slyke  has  had  quite  satisfactory  results  by 
combining  the  Gottlieb  and  Babcock  methods  as 
follows : 

"  Dissolve  lo  grams  of  milk  powder  in  lOO  c.  c. 
of  water.  Take  lo  c.  c.  of  this  solution  in  a  loo 
c.  c.  glass  cylinder.  Add  i  c.  c.  of  strong  ammonia 
and  shake  until  thoroughly  mixed  with  the  solution. 
Then  add  the  following  reagents,  one  after  the 
other,  shaking  vigorously  after  each  addition  be- 
fore adding  the  next  material :  lo  c.  c.  of  92  per  cent 
alcohol,  25  c.  c.  of  washed  ether,  and  25  c.  c.  of 
gasoline  or,  better,  petroleum  ether  (boiling  point 
below  80°  C).  The  cylinder  is  closed  with  a 
tightly  fitting,  moistened  cork  stopper.  The  con- 
tents of  the  cylinder,  after  thorough  shaking,  are 
poured  into  a  200  c.  c.  beaker,  the  cylinder  being 
rinsed  with  a  little  gasoline,  and  this  added  to  the 


ON   MILK  AND  MILK-TESTING  63 

beaker.  The  beaker  is  then  placed  on  a  steam  bath 
or  in  boiling  water,  and  kept  there  until  the  ether, 
alcohol,  and  gasoline  are  completely  evaporated. 
The  remaining  liquid  is  then  poured  into  a  milk- 
testing  bottle  and  the  beaker  is  rinsed  with  a  little 
ether,  which  is  also  added  to  the  test  bottle.  The 
test  bottle  is  then  placed  in  boiling  water  for  a  few 
minutes  to  evaporate  the  ether.  After  cooling  the 
contents  of  the  test  bottle  to  about  70°  F.,  add  17.5 
c.  c.  of  sulphuric  acid  and  complete  the  operation 
as  in  the  case  of  milk  by  the  Babcock  test.  The 
reading  is  multiplied  by  18.  In  some  cases,  as  in 
dried  skim  milk,  it  is  desirable  to  make  the  original 
solution  more  concentrated  by  having  20  or  more 
grams  in  100  c.  c.  of  solution. 

"  The  following  precautions  must  be  observed  in 
using  this  method : 

"  I.  The  milk  powder  solution  must  be  made 
uniform  before  sampling. 

"  2.  The  shaking  of  the  mixture  must  be  vigor- 
ous and  thorough  after  the  addition  of  each  of  the 
reagents  used. 

"  3.  The  evaporation  of  the  reagents  added  must 
be  complete,  otherwise  the  final  results  are  apt  to 
be  too  high. 

"4.  The  evaporation  must  not  be  carried  so  far 
as  to  cause  any  appearance  of  solid  particles  in  the 
liquid.  When  this  happens,  the  fat  column  con- 
tains darkened  material,  which  makes  the  results 
uncertain. 

"  This  method  is  applicable  to  skim  milk,  whey, 
and  buttermilk,  which  usually  do  not  give  high 
enough  results  by  the  Babcock  method." 


64  QUESTIONS   AND  ANSWERS 

Can  butter  be  tested  for  fat  by  the  Babcock  method? 
Yes;    but  not  with  as  much  accuracy  as  many 
other  dairy  products. 

How  is  butter  tested  for  its  fat  content? 

1.  By  the  ether  method.  Evaporate  a  known 
weight  (2  to  3  grams)  to  dryness  in  a  flat-bottom 
dish.  Then  wash  the  total  contents  of  the  dish 
upon  a  weighed  filter  paper,  using  about  50  c.  c.  of 
ether  or  naphtha.  Then  wash  free  from  fat  the 
residue  on  the  filter  paper  with  ether  or  naphtha. 
The  filter  is  then  dried  at  100°  C.  to  constant  weight 
and  weighed.  The  percentage  fat  is  determined  by 
the  difference  between  the  weight  of  butter  and  the 
weight  of  fat. 

2.  By  Babcock  test.  Weigh  4  grams  of  butter 
into  a  cream  bottle,  adding  enough  water  to  make 
18  grams  in  the  bottle.  Add  17.5  c.  c.  of  sulphuric 
acid  and  after  thoroughly  mixing  whirl  in  the  cen- 
trifuge for  five  minutes.  Add  hot  water  at  200°  F. 
to  raise  the  fat  in  the  graduated  neck  of  the  bottle. 
Whirl  again  for  two  minutes,  then  multiply  the 
reading  on  the  bottle  by  4.5. 

How  should  the  scale  be  read  in  testing  butter? 

The  same  as  in  testing  cream,  giving  credit  for 
that  part  of  the  scale  between  the  bottom  of  the 
fat  column  and  the  bottom  of  the  meniscus.  The 
temperature  of  the  fat  should  be  between  130°  and 
140°  F. 

What  is  meant  by  an  aliquot  part  of  a  quantity? 

It  is  the  part  that  results  from  dividing  a  quan- 
tity by  a  whole  number,  which  leaves  no  remainder. 


ON   MILK  AND   MILK-TESTING  t$ 

Example:    20  is  an  aliquot  of  100,  resulting  from 
the  division  of  100  by  5. 

How  may  a  representative  sample  of  cheese  be  se- 
cured for  the  fat  test? 
Where  possible,  cut  a  wedge-shaped  piece  reach- 
ing from  the  circumference  to  the  center  of  the 
cheese.  When  this  is  impossible,  three  plugs 
should  be  taken  with  a  trier  reaching  halfway  or  all 
the  way  through  the  cheese,  one  near  the  circum- 
ference, one  halfway  to  the  center,  and  the  third 
near  the  center.  In  either  case  the  sample  secured 
may  be  made  fine  by  passing  through  a  meat 
grinder  or  by  cutting  to  very  fine  pieces.  Thor- 
oughly mix  before  taking  the  sample. 

How  much  cheese  is  taken  for  the  test  and  how  is 
the  per  cent  calculated? 

^ix  grams  gives  good  results,  but  4.5  grams  or  9 
grams  may  bemused.  In  either  case,  when  the  ordi- 
nary cream  test  bottle  is  used,  to  obtain  the  per 
cent  of  fat  divide  18  by  the  weight  of  cheese  taken 
and  multiply  the  observed  reading  by  the  quotient. 
Example :  If  6  grams  of  cheese  were  taken  and  the 
observed  reading  was  12,  what  was  the  per  cent 
of  fat? 

I8-^6=3. 

i2X3=36=per  cent  of  fat. 

How  is  the  fat  in  cheese  determined  by  the  Babcock 

test? 

Weigh  into  a  cream  bottle  the  quantity  to  be 

used.     If  6  grams  are  taken,  add   12  c.  c.  of  hot 

water  to  make  18  grams  in  the  bottle,  shake  thor- 


66  QUESTIONS  AND  ANSWERS 

oughly,  let  stand  about  five  minutes  and  while  it  is 
still  quite  warm  add  17.5  c.  c.  of  sulphuric  acid.  It 
is  well  to  add  half  the  above  amount  of  acid  first, 
shake  thoroughly  and  then  add  the  remainder  and 
shake  until  the  casein  is  all  dissolved.  The  test 
is  then  completed  in  the  same  manner  as  for  cream 
or  butter. 

It  the  casein  in  the  fat  test  of  cheese  does  not  read- 
ily dissolve,  how  may  it  be  brought  into  solu- 
tion? 

1.  Let  the  cheese  soak  in  the  hot  water  in  the 
test  bottle  for  10  or  15  minutes  before  adding  the 
acid. 

2.  Have  the  mixture  of  cheese  and  water  quite 
hot  at  the  time  of  adding  the  acid  and  add  the 
acid  in  small  quantities,  shaking  between  each  addi- 
tion. 

3.  Add  an  excess  of  acid. 

Describe  the  Gerber  fat  test  for  milk. 

The  Gerber  test  depends  upon  the  same  prin- 
ciples for  separating  the  fat  that  are  used  in  the 
Babcock  fat  test.  Eleven  c.  c.  of  milk,  10  c.  c.  of 
sulphuric  acid  (specific  gravity  1.825)  and  i  c.  c. 
of  amyl  alcohol  are  used.  The  cork  is  inserted  and 
the  contents  of  the  bottle  thoroughly  mixed.  ^  The 
cork  should  then  be  forced  in  until  the  liquid  ex- 
tends well  into  the  narrow  graduated  neck  at  the 
ooposite  end  of  the  bottle.  The  mixture  is  centri- 
fuged  five  minutes,  the  bottles  resting  on  the 
corked  ends  meanwhile.  The  fat  column  is  then 
read  the  same  way  as  in  the  Babcock  test. 


ON    MILK  AND   MILK-TESTING  6^ 

How  is  the  Russian  Babcock  fat  test  bottle  con- 
structed ? 

The  bottle  consists  of  a  cylinder  and  a  graduated 
neck.  The  cylinder  is  about  an  inch  in  diameter 
and  55^  inches  long,  having  a  constriction  a  short 
distance  above  the  surface  of  the  liquid,  when  the 
milk  and  acid  are  mixed.  The  funnel-shaped  lower 
end  of  the  graduated  neck  rests  on  the  shelf  formed 
by  the  constriction,  while  the  upper  end  extends  a 
short  distance  out  of  the  cylinder. 

How  is  the  Russian  Babcock  fat  test  operated? 

The  neck  is  removed  from  the  bottle  while  adding 
the  milk.  It  is  replaced  before  whirling  the  bottle 
in  the  centrifuge.  After  whirling  for  five  minutes 
at  the  speed  proper  for  the  size  of  the  machine 
(usually  1,200  revolutions  per  minute),  hot  water 
is  added.  The  special  construction  of  the  machine 
and  the  bottle  make  it  possible  to  add  hot  water 
without  stopping  the  whirling.  The  bottle  is 
whirled  for  one  minute  after  adding  the  full  amount 
of  water.  The  per  cent  of  fat  is  read  as  in  the  regu- 
lar Babcock  fat  test. 


What  are  the  features  peculiar  to  the  Russian  Bab- 
cock fat  test? 

1.  A  specially  constructed  test  bottle. 

2.  The  use  of  one-half  the  amount  of  milk  and 
acid  taken  in  the  Babcock  fat  test. 

3.  A  specially  constructed  centrifuge,  enabling 
the  operator  to  add  hot  v/ater  without  stopping  the 
machine. 


68  QUESTIONS   AND  ANSWERS 

Give  four  formulas  used  in  determining  the  solids 
not  fat  in  milk. 

1  L+   7F    __  gQ^^is  j^Qt  fat. 

2  ^  +  .2  F  +  .14  =  solids  not  fat. 

4 

3  J  +  .2  F  =  solids  not  fat. 


L  +  F 


solids  not  fat. 


^         4 

In  each  of  these  formulas  L=lactometer  read- 
ing and  F=fat. 

How  do  the  results  secured  by  the  different 
formulas  compare? 

No.  I  gives  the  highest  results,  while  No.  3  gives 
the  lowest.  Nos.  2  and  4  give  about  the  same  re- 
sults excepting  on  rich  milks,  when  No.  4  gives 
results  that  are  nearly  as  high  as  those  secured 
with  formula  No.  i. 

With  what  class  of  milks  does  each  of  the  formulas 
give  best  results? 

Formula  No.  i  gives  results  that  correspond 
fairly  well  with  chemical  analysis  for  milks  having 
a  Quevenne  lactometer  reading  of  33  or  more  and 
having  more  than  4.5  per  cent  of  fat.  Formula 
No.  2  gives  its  best  results  in  milks  having  a 
Quevenne  reading  between  31  and  33  and  a  fat 
content  between  3.7  and  4.5  per  cent. 

Formula  No.  3  gives  best  results  on  all  milks 
having  a  Quevenne  reading  of  less  than  31  and  a 
fat  content  of  3.7  per  cent  or  less. 

Formula  No.  4  will  give  good  results  with  milk 
of  average  quality  or  richer  milks. 


ON    MILK   AND    MILK-TESTING  69 

How  may  the  per  cent  of  total  solids  be  deter- 
mined? 
By  adding  the  fat  as  determined  by  the  Babcock 
test  to  the  solids   not   fat,  as  determined  by  the 
application  of  the  formula. 

Is  there  a  formula  for  determining  the  per  cent  of 
protein  in  milk? 
The   following  formula  has  been  developed   by 
G.  A.  Olsen: 


TS-  A 


P 


3.694 

In  this  formula  T  S=total  solids,  A=ash,  and 
P=protein.  The  ash  is  to  be  called  .75  in  all 
cases. 

Below  what  percentage  do  the  solids  not  fat  of 
pure  milk  rarely  go? 
The  solids  not  fat  of  pure  milk  are  usually  more 
than  8.5  per  cent,  and  they  very  rarely  go  below 
8.4  per  cent. 

How  does  the  addition  of  water  to  milk  affect  the 
specific  gravity? 

Since  the  specific  gravity  of  water  is  less  than  the 
specific  gravity  of  milk,  the  addition  of  water  to 
milk  reduces  the  specific  gravity  of  the  mixture. 

How  does  the  skimming  of  milk  affect  its  specific 
gravity? 

Since  the  specific  gravity  of  the  fat  is  less  than 
the  specific  gravity  of  the  other  constituents  of 
milk,  skimming  increases  the  specific  gravity. 


yO  QUESTIONS  AND  ANSWERS 

Why  is  it  that  the  specific  gravity  is  not  a  sure 
indication  that  milk  has  been  neither  skimmed 
nor  watered? 

Because  a  sample  of  milk  might  be  skimmed,  or 
partly  skimmed,  and  then  just  water  enough  added 
to  reduce  the  specific  gravity  to  what  it  was  be- 
fore the  skimming  took  place ;  thus  there  would  be 
no  change  in  the  specific  gravity,  although  the  milk 
was  adulterated. 

What  is  the  approximate  proportion  of  fat  to  solids 
not  fat  in  normal  pure  milks? 
One  cannot  state  the  proportion  definitely,  since 
the  relative  quantity  of  the  constituents  in  milks 
from  different  cows,  breeds,  etc.,  varies.  In  gen- 
eral it  will  be  found  that  the  pure  milk  of  a  herd 
contains  fat  and  solids  not  fat  closely  approaching 
some  one  of  the  proportions  given  in  the  following 
table : 

Solids 
Fat  not  fat  Total  solids 

3.00  8.40  11.40 

3.25  8.47  11.72 

350  8-55  12.05 

3.75  8.62  12.37 

4.00  8.70  12.70 

4.25  8.77  13.02 

450  8.85  13.35 

4.75  8.92  13.67 

5.00  9.00  14.00 

5.25  9.07  14.32 

5.50  9-15  14.65 

5.75  9.22  14.97 

6.00  9.30  15.30 


ON    MILK  AND   MILK-TESTING  7I 

What  are  the   different  forms   of  adulteration  of 
milk  often  found? 

1.  Watering. 

2.  Skimming. 

3.  Watering  and  skimming. 

4.  The  addition  of  preservatives. 

5.  Addition  of  coloring  matter. 

6.  The  addition  of  acid  neutralizers. 

How  does  watering  affect  the  percentage  of  the 
different  milk  solids? 
It  reduces  the  percentage  of  all  the  milk  solids, 
and  reduces  them  in  the  same  proportion. 

How  does  skimming  affect  the  percentage  of  the 
milk  constituents? 

It  reduces  the  percentage  of  the  fat  and  slightly 
increases  the  percentage  of  all  other  constituents. 

How  may  the  presence  of  added  water  in  milk  be 
determined? 

Since  the  water  of  milk  has  the  same  chemical 
composition  as  pure  water  from  any  source,  and 
the  water  content  of  milk  varies  to  some  extent,  the 
presence  of  added  water  in  small  amounts  cannot 
be  determined  directly.  When  the  low  lactometer 
reading,  low  fat  content,  or  physical  characteristics 
of  the  milk  lead  one  to  suspect  that  it  is  adulter- 
ated a  control  sample  of  the  milk  as  produced  by 
the  cow  or  herd  should  be  procured  if  possible.  The 
composition  of  the  two  samples  should  be  com- 
pared. If  the  suspected  milk  is  to  any  great  extent 
lower  in  quality,  and  especially  if  the  per  cent  of 


72  QUESTIONS   AND  ANSWERS 

solids  not  fat  is  reduced,  it  is  safe  to  conclude  that 
the  milk  was  watered. 

If  a  sample  of  milk  gives  a  Quevenne  lactometer 
reading  of  29,  and  *is  found,  upon  testing  and 
applying  the  formula  for  solids  not  fat,  to  have 
4  per  cent  of  fat  and  8  per  cent  of  solids  not  fat, 
was  it  adulterated?     How  much,  and  what  was 
the  form  of  adulteration? 
One  may  conclude  that  any  milk  having  4  per 
cent  of  fat   should  have   at   least  8.6  per  cent  of 
solids  not  fat.     It  would  then  be  plain  that  the  milk 
was  watered,  since  the  solids  not  fat  are,  reduced 
approximately  7  per  cent,  determined  as  follows: 
8.6— 8=.6. 
.6-^8.6=.o697X  100=6.97  per  cent  of  added  water. 

How  may  one  detect  when  a  sample  of  milk  has 
been  skimmed? 

If  the  suspected  sample  has  a  low  percentage  of 
fat,  higher  lactometer  reading,  and  an  equal  or 
larger  percentage  of  solids  not  fat  than  the  control 
sample,  then  it  is  safe  to  conclude  that  the  milk 
was  skimmed. 

If  a  sample  of  milk  has  a  Quevenne  lactometer  read- 
ing of  33  and  contains  3  per  cent  of  fat,  was  it 
adulterated?  '  In  what  way  was  it  adulterated, 
and  how  much? 

Determine  the  solids  not  fat  by  the  formula : 

-^  +.2F=solids  not  fat. 

33-^4=8.25. 

3X.2=.6o. 

8.25+.6o=8.85^olids  not  fat. 


ON    MILK  AND   MILK-TESTING  73 

By  referring  to  the  table  given  in  answer  to  ques- 
tions on  page  70,  it  appears  that  milk  haying  8.85 
per  cent  of  solids  not  fat  should  contain  4.5  per  cent 
of  fat. 

4.5 — 3=1.5  per  cent  of  fat  missing. 

i-5^4.5=-3333X  100=33.33  per  cent  of  the  fat  re- 
moved by  skimming, 

How  may  one  detect  when  milk  has  been  skimmed 
and  watered? 
Milk  has  been  skimmed  and  watered  if  the  per- 
centage of  all  the  solid  constituents  are  reduced  and 
the  per  cent  of  fat  is  reduced  to  a  much  greater 
extent  than  the  other  solids. 

If  a  sample  of  milk  contains  2.8  per  cent  of  fat  and 
8.2  per  cent  of  solids  not  fat,  and  the  control 
sample  contains  4.5  per  cent  of  fat  and  8.85 
per  cent  of  solids  not  fat,  how  was  the  milk 
adulterated    and    what    was   the   per   cent    of 
adulteration? 
By    comparing   the    solids    not    fat   in    the    two 
samples   it  will   be   seen   that  the   milk   has  been 
watered,   because   the  solids  not  fat  are  reduced. 
Calculate  the  per  cent  of  added  water  by  determin- 
ing the  quantity  of  solids  displaced  by  it. 
8.85— 8.2=.65. 

.65 -f-8.85=.0734X  100=7.34  per  cent  of  added 
water. 

Next  determine  how  much  the  fat  is  reduced. 
4.5—2.8=1.7. 

1. 7-^-4.5=. 3777X100=37.7  per  cent  of  fat  miss- 
ing. 

Since  we  know  that  the  solids  not  fat  have  been 


74  QUESTIONS   AND  ANSWERS 

reduced  7.34  per  cent,  and  that  watering  reduces  all 
milk  solids  in  the  same  proportion,  it  follows  that 
the  fat  was  also  reduced  7.34  per  cent  by  watering. 
The  total  reduction  of  the  fat  minus  7.34  must  have 
been  lost  by  skimming. 

37-77— 7-34=30.43- 

Therefore,  the  milk  was  watered  7.34  per  cent, 
and  30.43  per  cent  of  the  fat  was  removed  by  skim- 
ming. 

How  should  a  factory  man  or  shipping  station 
agent  determine  whether  milk  has  been 
watered  or  skimmed  when  it  is  impossible  to 
secure  a  control  sample? 
First  determine  the  composition  of  the  suspected 
milk.  Then  compare  the  results  with  some  stan- 
dard. When  suspected  milk  is  furnished  by  an 
original  producer  it  usually  is  not  difficult  to  learn 
at  least  the  breed  of  cattle  producing  the  milk.  If 
the  herd  is  of  a  breed  that  produces  milk  of  a  high 
quality,  then  one  should  use  a  higher  standard  for 
comparison  than  in  the  case  where  the  milk  is  from 
a  herd  of  a  breed  that  naturally  produces  milk  of  a 
low  quality.  If  the  herd  is  composed  of  mixed 
breeds  or  common  stock  it  may  be  assumed  that 
the  pure  milk  is  of  average  quality.  To  judge  milk 
in  this  manner  would  be  a  difficult  problem  for 
one  having  no  experience  in  dairy  work,  but  an 
experienced  factoryman  or  agent  in  a  shipping 
station  should  have  little  trouble  in  gaining  in- 
f  )rmation  sufficient  to  w^irrant  a  fairly  reliable  con- 
clusion, 


ON    MILK   AND   MILK-TESTING  75 

If  a  sample  of  milk  contained  8.5  per  cent  of  solids 
not  fat  and  3.3  per  cent  of  fat,  should  it  be  con- 
sidered as  adulterated? 
If  one  -should  learn  that  the  milk  was  produced 
by  a  herd  of  Jersey  cows,  it  should  be  considered 
adulterated.  In  that  case  the  composition  of  the 
original  milk  would  be  at  least  4.4  per  cent  of  fat 
and  8.8  per  cent  of  solids  not  fat.  Those  figures 
could  be  used  as  a  basis  for  computing  the  kind  and 
amount  of  adulteration.  If  the  milk  was  produced 
by  a  Holstein  herd,  there  would  be  the  possibility 
that  it  was  adulterated  only  in  the  sense  that  a 
herd  of  cows  was  selected  which  gave  a  low  grade 
of  milk,  thus  bringing  the  quantity  of  total  solids 
below  the  legal  standard  of  12  per  cent.  If  such 
milk  was  sold  and  no  information  could  be  gained 
regarding  the  character  of  the  herd  producing  it, 
then  it  would  be  considered  as  having  been  actually 
adulterated. 

What  is  the  Hart  casein  test? 

It  is  a  method  of  testing  milk  for  the  percentage 
of  casein  it  contains. 

Upon  what  principles  is  the  Hart  casein  test  based? 

1.  That  dilute  acetic  acid  coagulates  casein  in  an 
insoluble  form  heavier  than  the  milk  serum. 

2.  The  ability  of  chloroform  to  extract  the  fat 
from  the  precipitated  casein  and  form  a  solution 
heavier  than  the  milk  serum  or  coagulated  casein. 

3.  Adopting  a  graduated  tube  and  a  volume  of 
milk  so  that  the  volume  of  collected  casein  indicates 
on  the  scale  the  percentage  of  casein  in  the  milk. 


76  QUESTIONS  AND  ANSWERS 

4.  Applying  centrifugal  force  to  separate  the 
serum,  the  casein,  and  the  chloroform  fat  solution. 

What  pieces   of  apparatus  are   used  in  the  Hart 
casein  test? 

1.  A  5  c.  c.  pipette  for  measuring  the  milk. 

2.  A  cylinder  holding  2  c.  c.  to  the  mark,  for 
measuring  the  chloroform. 

3.  A  strong  test  tube  5.6  inches  long.  About 
2.6  inches  of  one  end  is  formed  into  a  graduated 
neck  one-half  the  diameter  of  the  remainder,  which 
forms  the  body.  The  body  of  the  tube  should  hold 
35  c.  c.  and  the  graduated  part  exactly  5  c.  c.  Each 
graduation  on  the  scale  represents  .1  of  i  c.  c,  or  .2 
per  cent  of  casein.  The  opening  is  at  the  large  end 
of  the  tube. 

4.  A  strong  centrifuge  properly  constructed  for 
holding  the  test  tubes  and  geared  to  give  a  speed 
nearly  twice  as  great  as  would  be  required  in  a 
Babcock  fat  test  machine  having  a  revolving  disk 
of  the  same  size. 

5.  A  thermometer  for  determining  the  tempera- 
ture of  the  milk  and  acid  solution. 

What  reagents  are  used  in  the  Hart  casein  test? 

Dilute  acetic  acid  and  chloroform  of  the  best 
quality. 

How  much  and  of  what  strength  is  the  acetic  acid 
used  in  the  Hart  casein  test? 
Use  20  c.  c.  of  a  solution  containing  0.25  per  cent 
of  acetic  acid. 


ON   MILK  AND   MILK-TESTING  *jy 

How  may  an  acetic  acid  solution  of  proper  strength 
be  made? 

Add  to  lo  c.  c.  of  pure  glacial  acetic  acid  90  c.  c. 
of  water.  Take  25  c.  c.  of  this  solution  and  make 
it  up  to  1,000  c.  c.  by  the  addition  of  water.  The 
solution  then  contains  0.25  per  cent  of  acetic  acid. 

How  is  the  Hart  casein  test  carried  out? 

Add  2  c.  c.  of  the  chloroform,  20  c.  c.  of  the  dilute 
acid,  and  5  c.  c.  of  the  milk,  in  the  order  named,  to 
the  test  tube.  The  temperature  of  the  milk  and 
acid  solution  must  be  within  5°  of  70°  F.  A  lower 
temperature  tends  to  give  a  higher  reading,  and  a 
higher  temperature  has  the  reverse  eflfect.  The 
thumb  is  placed  over  the  opening  and  the  tube 
inverted  several  times  and  shaken  with  some  vigor 
for  not  more  than  20  nor  less  than  15  seconds.  The 
agitation  must  be  just  sufficient  to  thoroughly  mix 
the  contents  and  yet  not  form  an  emulsion.  The 
tubes  may  be  whirled  in  the  centrifuge  at  once  or 
may  stand  20  to  25  minutes  before  whirling,  if 
necessary.  The  speed  of  a  revolving  disk  15  inches 
in  diameter  should  be  approximately  2,000  revolu- 
tions per  minute,  and  should  continue  seven  and 
one-half  to  eight  minutes.  If  the  test  has  been 
properly  made  there  will  be  found  in  the  bottom  of 
the  tubes  on  taking  them  from  the  centrifuge  a 
layer  of  the  chloroform  fat  solution  and  immedi- 
ately over  it  the  layer  of  casein.  Allow  the  tubes 
to  stand  10  minutes  after  removing  from  the  ma- 
chines to  allow  the  casein  to  come  to  a  constant 
volume.    Then  read  the  test. 


78  QUESTIONS   AND  ANSWERS 

What  points   should   receive   special   attention   in 
making  the  Hart  casein  test? 

1.  The  temperature  of  the  milk  and  acid  solu- 
tion must  be  right. 

2.  The  mixture  must  be  shaken  properly  and  for 
the  right  length  of  time. 

3.  The  speed  of  the  centrifuge  must  be  sufficient, 
yet  not  too  great. 

4.  Allow  ten  minutes  to  elapse  after  complet- 
ing the  whirling  before  reading  the  test. 

What   coloring   matters   are    sometimes   added   to 
milk? 

1.  Annatto. 

2.  Coal-tar  colors. 

3.  Caramel. 

How  does  artificially  colored  milk  differ  in  appear- 
ance from  uncolored  milk? 
In  uncolored  milk  the  natural  yellow  is  contained 
largely  in  the  cream.  In  colored  milk  the  color 
remains  after  the  cream  has  risen  or  been  removed. 
The  skim  milk  does  not  show  the  familiar  bluish 
tint  when  coloring  matter  has  been  added. 

What  is  the  nature  of  annatto  coloring  matter? 

Annatto  is  a  reddish-yellow  coloring  matter  ex- 
tracted by  weak  alkaline  solutions  from  the  pulp 
inclosing  the  seeds  of  a  shrub  that  grows  in  South 
America  and  the  West  Indies.  The  alkaline  solu- 
tion is  used  for  coloring  purposes. 

Give  a  simple  test  for  annatto  coloring  in  milk. 
In    a    tig^htly    corked    vial    or    test    tube    shake 


ON    MILK  AND   MILK-TESTING  79 

vigorously  10  c.  c.  of  milk  and  an  equal  volume  of 
ether.  If  annatto  is  present  the  amount  will  be  in- 
dicated by  the  depth  of  the  yellow  coloring  in  the 
ether  layer  which  forms  on  the  surface  when  stand- 
ing quiet. 

How  may  foreign  color  be  detected  in  milk? 

The  following  method  was  developed  by  Leach: 

1.  Warm  about  150  c.  c.  of  milk  in  a  porcelain 
dish  and  add  about  5  c.  c.  of  acetic  acid,  after  which 
slowly  continue  the  heating  to  the  boiling  point 
while  stirring.  Gather  the  curd,  when  possible, 
into  one  mass  by  the  stirring  rod  and  pour  off  the 
whey.  If  the  curd  breaks  up  into  small  flakes, 
separate  from  the  whey  by  straining  through  a 
sieve.  Press  the  curd  free  from  adhering  liquid, 
transfer  to  a  small  flask,  and  macerate  for  several 
hours  (preferably  overnight)  in  about  50  c.  c.  of 
ether,  the  flask  being  tightly  corked  and  shaken  at 
intervals. 

2.  Detection  of  annatto  in  the  ether  extract. 
Decant  the  ether  as  obtained  above  into  an  evapo- 
rating dish  and  evaporate  the  ether  over  hot  water. 
Make  the  fatty  residue  alkaline  with  sodium  hy- 
droxide, and  pour  upon  a  very  small  wet  filter  while 
still  warm.  After  the  solution  has  passed  through, 
wash  the  fat  from  the  filter  with  a  stream  of  water 
and  dry  the  paper.  If,  after  drying,  the  paper  is 
colored  orange,  the  presence  of  annatto  is  indicated. 
Confirm  by  applying  a  drop  of  stannous  chlorid 
solution,  which,  in  the  presence  of  annatto,  produces 
a  characteristic  pink  on  the  orange-colored  paper. 

3.  Detection  of  coal-tar  color  ("  aniline  orange  ") 
in  the  curd.     The  curd  of  an  uncolored  milk  is  per- 


80  QUESTIONS  AND  ANSWERS 

fectly  white  after  complete  extraction  with  ether, 
as  is  also  that  of  milk  colored  with  annatto.  If  the 
extracted  fat-free  curd  is  distinctly  dyed  an  orange 
or  yellowish  color,  aniline  orange  is  indicated.  To 
confirm  the  presence  of  this  color,  treat  a  lump  of 
the  fat-free  curd  in  a  test  tube  with  a  little  strong 
hydrochloric  acid.  If  the  curd  immediately  turns 
pink,  the  presence  of  aniline  orange  is  assured. 

4.  Lythgoe's  test  for  aniline  orange  is  as  follows: 
Treat  about  10  c.  c.  of  the  milk  with  an  equal 

volume  of  hydrochloric  acid  (specific  gravity  1.20) 
in  a  porcelain  casserole  and  give  the  dish  a  slight 
rotary  motion.  If  an  appreciable  amount  of  aniline 
orange  is  present,  a  pink  color  will  at  once  be  im- 
parted to  the  curd  particles  as  they  separate. 

5.  Detection  of  caramel  (in  the  curd).  If  the 
fat-free  curd,  after  extraction  with  ether,  is  colored 
a  dull  brown,  caramel  is  to  be  suspected.  Shake 
a  lump  of  the  curd  with  strong  hydrochloric  acid  in 
a  test  tube  and  heat  gently.  In  the  presence  of 
caramel  the  acid  solution  will  gradually  turn  a  deep 
blue,  as  will  also  the  white  fat-free  curd  of  an  un- 
colored  milk,  while  the  curd  itself  does  not  change 
color.  It  is  only  when  this  blue  coloration  of  the 
acid  occurs  in  connection  with  a  brown  curd,  which 
itself  does  not  change  color,  that  caramel  is  to  be 
suspected,  as  distinguished  from  the  pink  colora- 
tion produced  at  once  under  similar  conditions  by 
aniline  orange. 

Name  several  of  the  preservatives  that  are  some- 
times used  in  milk. 

1.  Peroxides. 

2.  Borax  and  boric  acid. 


ON    MILK  AND   MILK-TESTING  8l 

3.  Formaldehyde. 

4.  Benzoates  and  benzoic  acid. 

5.  Carbonate  and  bicarbonate  of  soda. 

6.  Salicylic  acid. 

How  may  the  presence  of  peroxides  in  milk  be  de- 
tected? 

Add  to  15  or  20  c.  c.  of  milk  in  a  milk  test  bottle 
or  test  tube  a  quantity  of  paraphenylenediamin 
hydrochlorid  the  size  of  a  pea  and  shake  the  mix- 
ture vigorously  for  five  or  ten  seconds.  If  per- 
oxides are  present  the  milk  will  turn  blue  within 
a  few  minutes.  When  the  blue  solution  is  made 
alkaline  the  color  changes  to  a  yellowish  light  red. 
If  the  peroxide  has  been  in  the  milk  for  a  long  time, 
the  test  may  not  work  well. 

How  may  borax  or  boric  acid  in  milk  be  detected? 

To  50  c.  c.  of  the  milk  add  enough  sodium  hydrate 
to  make  alkaline.  Evaporate  the  solution  to  dry- 
ness and  incinerate.  Acidify  the  ash  with  a  small 
amount  of  strong  hydrochloric  acid.  A  strip  of 
tumeric  paper  is  then  soaked  in  the  solution  for  a 
few  minutes  -and  afterward  dried  on  a  clean  glass 
or  porcelain  surface.  If  the  paper  when  dry  is  a 
reddish  color  and  turns  to  a  dark  olive  green  on 
the  addition  of  dilute  ammonia,  the  presence  of 
boric  acid  or  borates  is  assured. 

How  may  the  presence  of  formaldehyde  in  milk  be 
detected? 

To  15  or  20  c.  c.  of  milk  in  a  Babcock  milk  test 
bottle  or  in  a  test  tube  add  4  or  5  drops  of  a  10  per 
cent  solution  of  ferric  chlorid.  Then  add  a  volume  of 


82  QUESTIONS  AND  ANSWERS 

sulphuric  acid  equal  to  the  volume  of  milk  taken. 
Shake  the  bottle  in  a  circle,  but  not  sufficient  to 
mix  the  milk  and  acid  to  any  great  extent.  In  the 
presence  of  formaldehyde  a  deep  bluish-violet  color- 
ation appears  in  the  circle  where  the  milk  and  acid 
join.  Hydrochloric  acid  having  a  specific  gravity 
of  1.2  may  be  substituted  for  sulphuric  acid  in  the 
test. 

How  may  the  presence  of  carbonates  in  milk  be  de- 
tected? 

1.  The  ash  of  milk  containing  carbonates  will 
effervesce  upon  the  addition  of  a  few  drops  of 
diluted  hydrochloric  acid.  This  is  a  strong  indica- 
tion of  added  carbonates. 

2.  Add  to  lo  or  15  c.  c.  of  the  milk  an  equal 
volume  of  alcohol  and  a  few  drops  of  a  i  per  cent 
solution  of  rosalic  acid.  In  the  presence  of  car- 
bonates a  rose-red  color  appears,  while  pure  milk 
shows  a  light  yellowish-red  color. 

How  may  the  presence  of  benzoic  acid  in  milk  be 
detected  ? 
Add  5  c.  c.  of  dilute  hydrochloric  acid  to  50  c.  c. 
of  the  milk  in  a  flask  and  shake  to  curdle.  Extract 
the  curdled  milk  with  successive  portions  of  ether. 
Transfer  the  ether  to  a  separatory  funnel  and  shake 
with  dilute  ammonia,  which  separates  the  benzoic 
acid  from  the  fat,  in  the  form  of  ammonium  ben- 
zoate.  Draw  off  the  ammoniacal  solution  and 
evaporate  in  a  dish  over  hot  water  until  all  free 
ammonia  has  disappeared,  but  before  dryness  is 
reached  add  a  few  drops  of  ferric  chlorid  reagent. 
A  flesh-colored  precipitate   indicates  benzoic  acid. 


ON    MILK  AND   MILK-TESTING  83 

All  free  ammonia  should  be  driven  off,  otherv/ise 
ferric  hydrate  would  be  formed. 


How  may  the  presence  of  salicylic  acid  in  milk  be 
detected? 

The  acid  is  seldom  used  as  a  preservative  in  milk. 
If  its  presence  is  suspected,  proceed  exactly  as  in 
testing  for  benzoic  acid.  On  applying  the  ferric 
chlorid  to  the  solution  after  the  evaporation  of  the 
ammonia  a  violet  color  indicates  the  presence  of 
salicylic  acid. 

How  can  the  presence  of  starch  in  milk  be  de- 
tected? 

To  10  or  15  c.  c.  of  milk  in  a  test  tube  or  vial  add 
a  few  drops  of  an  iodine  solution.  If  starch  is 
present  it  will  be  colored  blue  by  the  iodine. 

How  may  milk  that  has  been  heated  to  175°  F.  be 
detected? 

1.  To  15  or  20  c.  c.  of  milk  in  a  small  bottle  or 
test  tube  add  i  c.  c.  of  a  concentrated  starch  solu- 
tion and  6  or  8  drops  of  a  10  per  cent  solution  of 
potassium  iodid.  Next  add  4  or  5  drops  of  a  2  per 
cent  solution  of  hydrogen  peroxid.  Upon  shak- 
ing the  mixture  it  will  turn  to  a  dark  blue  color  if 
the  milk  has  not  been  heated  to  175°  F. 

2.  In  the  same  manner  as  above,  add  a  quantity  of 
paraphenylenediamin  hydrochlorid  about  the  size 
of  a  pea  and  4  or  5  drops  of  a  2  per  cent  solution 
of  hydrogen  peroxid.  The  mixture  turns  blue  on 
shaking  if  the  milk  has  not  been  heated  to  175°  F. 


84  QUESTIONS  AND  ANSWERS 

What  causes  the  color  of  the  milk  to  change  in  the 
tests  for  heated  milk? 

The  enzymes  of  the  milk  set  free  oxygen  from 
the  hydrogen  peroxid  and  the  free  oxygen  sets 
free  iodine  from  the  potassium  iodid.  Then  the 
free  iodine  colors  the  starch  blue.  When  the 
enzymes  are  destroyed  by  heat  no  action  takes 
place  and  the  milk  remains  white. 

In  the  second  test  the  oxygen,  set  free  by  the 
enzymes,  acts  upon  the  other  reagent,  causing  it  to 
change  to  a  blue  color. 

What  are  the  common  ways  of  adulterating  cream? 

1.  By  diluting  the  cream  with  milk. 

2.  By  the  addition  of  thickeners. 

3.  By  the  addition  of  preservatives. 

4.  By  the  addition  of  acid  neutralizers. 

How  may  the  tendency  to  dilute  the  cream  be  over- 
come? 
By  buying  and  selling  cream  upon  the  basis  of 
the  fat  content. 

How  may  the  presence  of  condensed  milk  or  con- 
densed skim  milk  in  cream  be  detected? 

Separate  the  fat  of  the  cream  from  the  serum. 
Determine  the  per  cent  of  solids  not  fat  in  the 
serum.  If  the  serum  contains  a  greater  percentage 
of  milk  solids  not  fat  than  is  found  in  skim  milk, 
the  presence  of  condensed  milk  or  condensed  skim 
milk  is  assured. 

How  may  the  presence  of  gelatin  in  cream  be  de- 
tected? 


ON    MILK   AND  MILK-TESTING  85 

Prepare  an  acid  solution  of  mercuric  nitrate  by- 
dissolving  mercury  in  twice  its  weight  of  nitric  acid 
of  1.42  specific  gravity,  and  diluting  the  solution  to 
25  times  its  bulk  with  water.  To  10  c.  c.  of  the 
cream  to  be  examined,  add  an  equal  volume  of 
acid  mercuric  nitrate  solution,  shake  the  mixture, 
add  20  c.  c.  of  water,  shake  again,  allow  to  stand 
five  minutes,  and  filter.  If  much  gelatin  is  present 
the  filtrate  will  be  opalescent  and  cannot  be  ob- 
tained very  clear.  To  a  portion  of  the  filtrate  con- 
tained in  a  test  tube  add  an  equal  volume  of  a 
saturated  aqueous  solution  of  picric  acid.  A  yellow 
precipitate  will  be  produced  in  the  presence  of  any 
considerable  amount  of  gelatin,  while  smaller 
amounts  will  be  indicated  by  a  cloudiness.  In  the 
absence  of  gelatin  the  filtrate  obtained  will  be  per- 
fectly clear.  The  test  will  work  equally  well  for 
determining  the  presence  of  gelatin  in  milk. 

How  may  the  presence  of  starch  in  cream  be  de- 
tected? 
By  adding  a  small  amount  of  iodine  solution  as 
in  the  test  for  starch  in  milk.  A  slightly  larger 
quantity  of  the  iodine  solution  should  be  added,  as 
the  greater  amount  of  fat  in  cream  will  absorb 
more  of  the  iodine. 

What  substances  are  often  used  as  cream  thicken- 
ers? 

1.  Sucrate  of  lime  (viscogen). 

2.  Condensed  milk  or  condensed  skim  milk. 

3.  Gelatin. 

4.  Starch. 


S6  QUESTIONS  AND  ANSWERS 

How  is  sucrate  of  lime  made? 

Slake  3  pounds  of  freshly  burned  lime  in  hot 
water.  Make  the  quantity  up  to  5  gallons  by  add- 
ing water.  Dissolve  10  pounds  of  sugar  in  five 
gallons  of  water.  Mix  the  two  solutions  and  stir 
at  intervals  for  about  three  hours.  Let  settle  and 
use  the  clear  solution. 

How  may  the  presence  of  viscogen  in  cream  be 
detected? 

Determine  the  number  of  c.  c.  of  -f^  acid  re- 
quired to  neutralize  the  ash  from  100  grams  of  the 
cream.  The  -^  acid  should  be  added  in  excess 
and  titrated  back  with  -^  alkali.  If  more  than 
14  c.  c.  are  required  it  is  a  strong  indication  that 
viscogen  is  present  in  the  cream. 

How  may  the  presence  of  preservatives  in  cream 
be  detected? 
The  methods  used  for  detecting  preservatives  in 
milk  may  be  applied  to  cream  as  well.  In  some 
cases  it  may  be  necessary  to  dilute  the  cream  before 
applying  the  tests. 

How  may  the  presence  of  acid  neutralizers  in  cream 
be  detected? 

The  substances  used  to  neutralize  the  acid  are 
alkalies  or  carbonates  and  the  methods  for  detecting 
them  are  the  same  as  those  used  on  milk. 

How  is  butter  sometimes  adulterated? 

1.  By  substituting  a  foreign  fat  for  the  whole  or 
a  part  of  the  butter  fat. 

2.  By  selling  renovated  butter  as  fresh  butter. 


ON   MILK  AND   MILK-TESTING  87 

3.  By  incorporating  an  excess  of  moisture  dur- 
ing the  process  of  manufacture. 

4.  By  the  addition  of  preservatives. 

How  may  renovated  butter  and  oleomargarine  be 
distinguished  from  butter? 

1.  Melt  some  of  the  substance  in  a  spoon  by 
holding  it  over  a  small  flame.  Let  the  melted  fat 
boil  vigorously.  Renovated  butter  and  oleomar- 
garine snap  and  sputter  with  noise  while  boiling 
and  very  little,  if  any,  foam  is  formed.  In  boiling, 
butter  makes  little  noise  and  a  large  amount  of 
foam  forms. 

2.  On  melting  butter  and  allowing  the  casein 
and  water  to  settle  a  transparent  oil  results.  With 
oleomargarine  or  renovated  butter  the  oil  remains 
cloudy. 

How  may  renovated  butter  and  oleomargarine  be 
distinguished? 
Heat  about  half  a  pint  of  milk  in  a  tin  cup  to 
140°  F.  Add.  to  this  a  tablespoonful  of  the  sub- 
stance. Stir  with  a  wooden  stirring  rod  until 
melted.  Then  set  the  cup  in  ice  cold  water  and 
stir  until  the  fat  hardens.  It  may  then  be  collected 
into  a  lump  with  the  wooden  stirring  rod  if  it  is 
oleomargarine,  but  will  remain  separated  in  fine 
granules  if  it  is  butter  or  renovated  butter. 

What  is  one  of  the  best  methods  for  distinguishing 
butter  from  oleomargarine? 

By  determining  the  Reichert-Meissl  number. 


88  QUESTIONS  AND  ANSWERS 

What  is  meant  by  the  Reichert-Meissl  number? 

It  means  the  number  of  c.  c.  -^  alkali  required 
to  neutralize  the  volatile  acids  from  5  grams  of  the 
fat. 

How  is  the  Reichert-Meissl  number  determined? 

Five  grams  of  the  fat  are  placed  in  a  clean,  dry- 
flask  of  300  c.  c.  capacity,  10  c.  c.  of  95  per  cent 
alcohol  added,  and  2  c.  c.  of  a  saturated  aqueous 
solution  of  sodium  hydrate.  Place  a  funnel  in 
the  neck  of  the  flask  and  heat  on  the  water  bath 
with  occasional  shaking  until  saponification  is  com- 
plete, when  the  solution  will  be  free  from  fat-glob- 
ules and  perfectly  clear.  Then  remove  the  funnel 
and  continue  heating  over  the  bath  to  dryness. 
Add  135  c.  c.  of  water  and  warm  on  the  water  bath 
with  shaking  until  the  soap  is  dissolved.  Cool  and 
add  a  few  small  pieces  of  pumice  stone,  to  prevent 
lumping  while  boiling,  and  5  c.  c.  of  dilute  sul- 
phuric acid  (200  parts  of  acid  to  1,000  parts  water). 
Connect  the  flesk  with  a  condenser  and  distill  oflF 
no  c.  c.  in  about  30  minutes.  Titrate  the  entire 
distillate  with  tenth-normal  alkali,  using  phenol- 
phthalein  as  indicator.  The  number  of  cubic  cen- 
timeters of  tenth-normal  alkali  required  express 
what  is  called  the  Reichert-Meissl  number. 

How  does  the  Reichert-Meissl  number  for  butter 
and  for  oleomargarine  differ? 

The  size  of  the  Reichert-Meissl  number  for  oleo- 
margarine usually  depends  to  a  great  extent  upon 
the  per  cent  of  butter  present  in  the  oleomargarine. 
This  number  is  not  often  more  than  5  for  oleomar- 
garine  and   rarely   less   than   24  for   butter.     The 


ON    MILK  AND   MILK-TESTING  89 

Reichert-Meissl  number  for  butter  is  usually  be- 
tween 24  and  31. 

What  fats  are  sometimes  used  to  adulterate  butter? 
Lard  and  beef  fat  or  products  manufactured 
therefrom,  as  lard  stearin  and  beef  stearin.  Stearin 
derived  from  cottonseed  oil  is  also  used.  Fats  or 
oils  from  any  source  may  be  used  provided  they 
have  the  proper  melting  point  when  mixed  and  no 
strong  flavors. 

What  fats  are  used  in  the  manufacture  of  oleo- 
margarine? 

Neutral  lard,  beef  fat  stearin  and  cottonseed  oil 
stearin  are  the  principal  fats  used  in  nearly  all  the 
oleomargarine  now  manufactured.  Cottonseed  oil 
stearin  is  probably  not  used  to  so  great  an  extent  as 
the  others.  Small  quantities  of  a  few  other  oils 
are  sometimes  added  to  change  the  color  to  more 
nearly  resemble  that  of  butter. 

What  is  neutral  lard  and  lard  stearin? 

Neutral  lard  is  the  best  quality  of  lard  made 
from  hog  fat.  The  fat  is  rendered  at  a  low  tem- 
perature and  the  product  washed  with  water  con- 
taining a  little  sodium  carbonate,  salt,  or  dilute 
acid.  The  product  then  has  only  a  slight  acidity 
and  is  almost  tasteless.  Its  principal  use  is  in  the 
manufacture  of  oleomargarine.  Lard  stearin  is 
made  by  melting  lard  and  holding  it  at  a  tempera- 
ture between  50°  and  60°  F.,  until  the  stearin  sep- 
arates in  crystals.  It  is  then  filtered  and  pressed 
in  cloth  sacks.  The  oil  obtained  is  used  for  illumi- 
nating   and    lubricating    purposes.       The    stearin 


90  QUESTIONS  AND  ANSWERS 

which  is  collected  in  the  sacks  is  mixed  with  other 
fats  and  manufactured  into  oleomargarine  or  com- 
pounds like  lard  and  cottonseed  oil. 

How  is  oleomargarine  manufactured? 

The  process  of  manufacture  depends  somewhat 
upon  the  ingredients  used  and  the  markets  to  be 
supplied.  When  the  product  goes  to  a  tropical 
country  oils  of  higher  melting  points  are  used  in 
larger  quantity  than  when  the  product  goes  to 
colder  climates.  In  general  the  oleo  oil  from  beef 
tallow,  the  neutral  lard  or  lard  stearin  from  hog 
fat,  and  the  cottonseed  oil  stearin  are  mixed  in  pro- 
portions giving  a  melting  point  about  that  of  butter. 
The  mixture  is  then  churned  with  skim  milk  or 
whole  milk  and  the  process  thereafter  is  practically 
the  same  as  that  for  the  making  of  butter  from 
cream. 

What  preservatives  may  be  used  in  butter? 

1.  Boric  acid  or  borates. 

2.  Formaldehyde. 

3.  Salicylic  acid. 

4.  Sulphurous  acid. 

How  may  the  presence  of  boric  acid  or  borates  be 
detected  in  butter? 

Melt  an  ounce  or  two  of  the  butter  at  the  tem- 
perature of  boiling  water  and  collect  the  aqueous 
solution  at  the  bottom.  To  a  small  amount  of  the 
aqueous  solution  add  a  few  drops  of  hydrochloric 
acid.  Then  apply  tumeric  paper  to  the  liquid.  If 
the  paper  turns  red  upon  drying  and  turns  to  a  dark 


ON    MILK  AND   MILK-TESTING  9I 

olive  green  upon  being  made  alkaline  with  ammonia 
the  presence  of  boric  acid  is  assured. 

How  may  the  presence  of  formaldehyde  in  butter 
be  detected? 

Melt  the  butter  at  a  low  temperature  and  sep- 
arate some  of  the  water  solution  that  collects  at 
the  bottom.  To  this  add  milk  free  of  formaldehyde. 
Then  test  the  mixture  for  formaldehyde  by  adding 
a  few  drops  of  ferric-chlorid  solution  and  con- 
centrated sulphuric  or  hydrochloric  acids,  as  in  the 
case  with  milk.  A  violet  blue  color  assures  the 
presence  of  formaldehyde. 

How  may  the  presence  oi  salicylic  acid  in  butter  be 
detected? 

Separate  some  of  the  water  solution  that  settles 
to  the  bottom  on  melting  the  butter  and  follow  the 
directions  given  for  the  detection  of  salicylic  acid  in 
milk. 

How  may  the  presence  of  sulphurous  acid  in  butter 
be  detected? 

Separate  some  of  the  water  solution  that  settles 
out  on  melting  the  butter.  Distill  off  a  part  of  it 
and  to  the  distillate  add  bromine  water  and  barium 
chlorid.  A  precipitate  indicates  the  presence  of 
sulphurous  acid  or  a  sulphite  in  the  butter. 

How  is  butter  tested  for  its  salt  content? 

I.  Weigh  into  a  glass  beaker  10  grams  of  butter. 
Add  about  20  c.  c.  water.  Warm  it  to  melt  the 
butter  and  then  transfer  the  butter  and  water  to  a 
separatory  funnel.     Insert  the  stopper.     Shake  for 


92  QUESTIONS  AND  ANSWERS 

a  few  moments.  Allow  the  mixture  to  stand  a  few 
minutes  until  any  remaining  fat  has  collected  on 
the  surface.  Then  draw  the  water  into  a  flask,  being 
sure  that  no  fat  passes  through.  Again  add  hot 
water  to  the  beaker  and  repeat  the  washing  in  the 
funnel  several  times,  using  15  c.  c.  of  water  each 
time. 

Determine  the  sodium  chlorid  in  a  measured 
part  (10  c.  c.)  of  the  liquid  by  titrating  with  stand- 
ard silver  nitrate  solution,  using  potassium  chro- 
mate  as  an  indicator,  i  c.  c.  -g-  silver  nitrate  solu- 
tion=.oo5837  grams  of  salt. 

To  determine  the  total  amount  of  salt  divide  the 
total  number  c.  c.  of  water  used  by  10  and  multiply 
by  .005837.  This  will  give  the  total  number  grams 
of  salt  in  10  grams  of  butter.  Then,  knowing  the 
amount  present  in  10  grams,  it  is  an  easy  matter  to 
determine  the  amount  in  100  grams  by  multiplying 
by  10.  This  gives  the  percentage  of  salt  in  the 
butter  tested. 

2.  Gray's  salt  test.  A  representative  lo-gram 
sample  of  butter  is  placed  in  a  small  glass  dish. 
The  dish  is  then  half  filled  with  boiling  water  and 
the  mixture  of  fat  and  water  poured  into  a  500  c.  c. 
glass  flask.  The  dish  is  rinsed  several  times  with 
hot  water  and  each  time  the  rinsings  are  poured  into 
the  flask.  The  flask  is  then  filled  to  the  500  c.  c. 
mark  with  boiling  water  and  thoroughly  shalcen. 
Then  allow  the  contents  of  the  flask  to  cool  and 
after  the  fat  has  collected  on  top  and  hardened, 
measure  with  a  pipette  50  c.  c.  of  the  clear  solution 
beneath  the  fat  and  place  it  in  a  clean  glass  dish. 
Fifty  c.  c.  of  a  potassium  chromate  indicator  is 
then  added  and  the  solution  titrated  with  a  standard 


ON   MILK  AND  MILK-TESTING  93 

silver  nitrate  solution.  The  strength  of  this  silver 
nitrate  solution  is  such  that  i  c.  c.  of  it  represents 
one-tenth  of  i  per  cent  of  salt. 

3.  The  Fitch  salt  test.  A  representative  3.5- 
gram  sample  of  butter  is  placed  in  a  300  c.  c.  glass 
flask  and  180  c.  c.  of  boiling  water  added.  The 
flask  is  then  corked  and  thoroughly  shaken,  care 
being  taken  to  remove  the  cork  often  tt)  relieve  the 
pressure.  The  mixture  is  then  allowed  to  cool  and 
after  the  fat  has  collected  on  the  top  and  solidified 
17.6  c.  c.  of  the  clear  solution  beneath  the  fat  is 
placed  in  a  white  cup.  Then  17.6  c.  c.  of  potassium 
chromate  indicator  is  added  and  the  solution 
titrated  with  a  standard  silver  nitrate  solution  meas- 
ured from  a  graduated  cylinder  till  the  solution  be- 
comes a  permanent  reddish  color.  The  number 
c.  c.  silver  nitrate  used  divided  by  io=per  cent  salt. 

How  is  the  moisture  content  of  butter  determined? 

1.  By  chemical  analysis. 

2.  By  practical  moisture  tests. 

What  are  the  names  of  the  more  commonly  used 
moisture  tests? 

1.  Cornell  test. 

2.  Mitchell-Walker. 

3.  Irish. 

4.  Gray's. 

5.  Farrington. 

How  should  a  representative  sample  of  butter  be 
secured  and  prepared  for  making  a  moisture, 
salt,  or  fat  test? 
From  the  mass  of  butter  to  be  tested  take  several 


94  QUESTIONS  AND  ANSWERS 

samples  from  various  parts.  The  samples  when 
added  together  should  make  about  6  ounces.  These 
are  placed  in  a  wide-mouth  sample  bottle  or  fruit 
jar  and  placed  in  hot  water  until  the  butter  melts  to 
the  consistency  of  thin  cream.  While  melting,  the 
butter  should  be  thoroughly  and  continuously 
stirred  with  a  table  knife  or  similar  instrument. 
The  bottle  should  then  be  well  shaken  to  secure  a 
uniform  mixing  of  the  sample.  The  bottle  is  then 
placed  in  cold  water  to  solidify,  but  while  cooling 
the  butter  should  be  stirred  continuously.  As  soon 
as  the  butter  has  become  fairly  solid  or  plastic,  the 
sample  for  testing  can  be  secured.  If  in  melting 
the  butter  becomes  oily  great  care  and  skill  must 
be  used  to  reincorporate  the  water  evenly  during 
cooling. 

Describe  and  give  directions  for  using  the  Irish 
moisture  test. 
A  representative  lo-gram  sample  of  butter  is 
placed  in  a  small  metal  cup  and  held  over  a  flame 
with  a  pair  of  special  forceps  until  all  the  moisture 
has  evaporated  from  it.  While  the  butter  is  heat- 
ing it  foams  considerably.  As  soon  as  the  foaming 
has  ceased,  and  before  the  fat  begins  to  char,  a 
small  mirror  is  held  over  the  cup  to  show  if  any 
moisture  still  remains.  When  the  sample  is  thus 
freed  from  moisture  it  is  cooled  to  room  tempera- 
ture, 60°  F.  to  70°  F.,  and  reweighed  upon  a  special 
scale  by  which  the  difference  between  the  weight 
of  the  butter  before  and  after  heating  is  indicated 
in  the  form  of  percentage  by  the  use  of  small 
weights. 


ON  MILK  AND  MILK-TESTING  95 

Describe  and  give  directions  for  using  Gray's 
moisture  test. 

This  test  consists  of  a  scale,  glass  flask,  gradu- 
ated glass  tube,  condenser,  amyl  reagent,  and  an 
alcohol  lamp. 

A  representative  lo-gram  sample  of  butter  is 
placed  in  the  glass  flask.  To  this  6  c.  c.  of  amyl  re- 
agent is  added  and  the  different  parts  of  the  test 
then  connected  for  use.  The  condenser  is  filled 
with  cold  water.  The  butter  and  amyl  mixture  is 
heated  over  a  flame,  the  moisture  is  driven  off  and 
collects  in  the  graduated  glass  tube,  where  it  can  be 
read  in  the  form  of  percentage.  The  heating  is 
stopped  as  soon  as  the  mixture  in  the  flask  becomes 
brown  and  the  crackling  noise  ceases.  This  usually 
requires  about  six  minutes. 

Should  heat  be  applied  too  severely  to  the  flask 
the  steam  may  go  above  the  15  per  cent  mark. 
This  should  be  prevented  by  withdrawing  the  heat 
for  a  short  time.  Great  care  must  be  exercised  in 
collecting  all  the  moisture  in  the  graduated  tube  if 
reliable  readings  are  to  be  secured. 

Describe  and  f^ive  directions  for  using  Farrington*s 
moisture  test. 
In  Farrington's  test  10  grams  of  a  representative 
sample  of  butter  is  placed  in  a  small  dish.  The 
dish  is  then  placed  in  a  special  oven  heated  to  from 
240°  F.  to  270°  F.  under  steam  pressure.  Here  the 
butter  is  left  until  all  moisture  has  been  evaporated, 
indicated  by  the  browning  of  the  casein  in  sample. 
This  usually  takes  about  30  minutes.  After  the 
moisture  has  been  evaporated  the  dish  and  its  con- 
tents  is   reweighed   and   the   difference   from   the 


g6  QUESTIONS  AND  ANSWERS 

original  weight  determined.  The  per  cent  moisture 
can  thus  be  easily  determined.  Occasionally  a  re- 
verse beam  scale  is  used  upon  which  the  per  cent 
moisture  evaporated  can  be  read  direct. 

Describe  and  give  directions  for  using  the  Cornell 
moisture  test 

This  is  a  simple,  accurate,  and  durable  test  re- 
cently prepared  by  Mr.  H.  E.  Ross  of  the  dairy- 
department  of  the  New  York  state  college  of  agri- 
culture. The  test  resembles  the  Irish  test,  but  has 
several  important  improvements. 

A  lo-gram  sample  of  butter  is  secured  in  the 
usual  way.  This  is  placed  in  a  special  cast  alum- 
inum cup  and  the  cup  held  over  a  flame  with  special 
forceps  or  placed  on  some  heated  surface.  The 
important  features  of  the  test  are  the  use  of  this  cup 
and  the  use  of  a  thin  sheet  of  asbestos  between 
flame  or  heated  surface  and  the  cup.  The  asbestos 
prevents  all  the  sputtering  of  the  heating  butter  and 
eliminates  a  great  deal  of  the  danger  of  charring. 
The  sample  is  heated  till  all  moisture  is  driven  off. 
This  usually  requires  about  25  minutes,  and  is  in- 
dicated by  the  casein  losing  its  snow-white  color 
and  becoming  brown.  The  sample  is  then  cooled 
and  reweighed  with  a  special  scale  upon  which  the 
per  cent  moisture  can  be  read  directly  and  accu- 
rately. 

Describe  and  give  directions  for  using  the  Mitchell- 
Walker  test 
The  apparatus  in  this  test  consists  of  a  meial 
evaporating   cup,   condenser,   graduated   glass   re- 
ceiver, scale  for  weighing  sample,  spirit  lamp,  amyl 


ON   MILK  AND  MILK-TESTING  97 

acetate  reagent,  and  a  stand  to  support  the  appa- 
ratus. 

A  representative  lo-gram  sample  of  butter  is 
placed  in  the  metal  cup.  To  this  is  added  10  c.  c. 
of  the  amyl  acetate  reagent.  The  apparatus  is 
then  connected  and  the  condenser  filled  with  cold 
water.  The  alcohol  flame  is  then  applied  under 
the  evaporating  cup.  In  about  a  minute  the  water 
and  reagent  will  begin  to  pass  over  and  drop  from 
the  condenser  tube  into  the  receiver.  After  all  the 
water  has  been  evaporated  from  the  cup,  the  reagent 
will  cease  dropping  for  a  moment  and  then  begin 
again  as  soon  as  it  has  reached  its  own  boiling 
point,  which  is  higher  than  that  of  the  water.  Con- 
tinue to  apply  the  flame  until  practically  all  the  re- 
agent is  driven  oif  and  it  ceases  to  drop  freely  from 
the  condenser  tube.  By  this  means  all  the  water 
is  washed  out  of  the  condenser  tube  and  the  major 
portion  of  the  reagent  is  recovered.  The  flame  is 
now  extinguished.  The  mouth  of  the  receiver  is 
corked  and  taken  by  the  top  and  shaken  a  few 
times  to  detach  any  drops  of  water  that  may 
adhere  to  the  sides. 

The  per  cent  moisture  can  now  be  read  in  the 
graduated  receiver.  The  water  is  withdrawn  from 
the  receiver,  and  then  the  reagent,  which  is  collected 
in  a  bottle  and  preserved  for  use  in  later  tests. 


INDEX 


Paga 

Acid 

measures 43 

sulphiiric 43 

sulphtirous 91 

tests  for li  5,  6 

Babcock  test 33,  39 

Bacteria    12 

Butter 

adulterations   89 

preservatives 90 

sampling 6S 

testmg 65 

Buttermilk    17,  57 

Calibrating 

cream  bottles 41 

nlilk  bottles 40 

Casein 3 

Cheese 

sampling 65 

testing 65 

Colostrum 

composition  of 9 

tests  for 10 

Cream 

adulteration 84 

sampling   51,  57 

testmg 51 

thickeners 85 

Ferments    11 

Formulas 

protein    69 

solids  not  fat 68 

Gerber  fat  test 66 

Lactometers 27 

Lactoscopes   31 

Mammary  gland 7 

Milk 

adulteration    69,  74 

aerated   17 

carbonated 19 

clarified 18 

color    10 

composition  of 1,     2,  10 

condensed 19 

contamination 14,  15 

diseases 14 

drinks   17 

electrified   18 

fat 3,  4 

human 1 

malted 19 

market    17 


Milk — Continued 

modified   18 

pasteurized 18 

peptonized  19 

powdered    20 

sampling 47 

sanitary 17 

secretion    8,  9 

serum 10,  23 

standardized 20 

sugar 2 

tests 6 

water 2 

weight  of 23 

Oleomargarine 

manufacture 90 

tests  for 87 

Pasteurization 16 

Preservatives    48,  80 

Reichert-Meissl  ntmiber 88 

Score  cards 24,  25 

Specific    gravity 22,  23,  26 

Spores    11,  12 

Sterilization 16 

Tests 

acid , 1,  5,  6 

albtunin    3 

annatto 78 

benzoic  acid 82 

boracic  acid 81 

carbonates   82 

casein    75 

condensed  milk 60,  61 

fat 66,  67 

foreign   color 79 

formaldehyde 81 

gelatin     84 

moisttire 92,  95 

oleomargarin 87 

pasteurized  milk 83 

peroxides    81 

renovated  butter 87 

salicylic  acid 83 

salt 91 

skimmed  milk 57 

starch    83 

sucrate  of  lime 86 

sulphurous  acid 91 

viscogen    86 

whey 57 

Viscogen ••  8^ 


